Patent Publication Number: US-RE41329-E

Title: Machining apparatus for workpiece and method therefor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a polishing machining apparatus and a machining method for machining a workpiece to be polished where a plurality of magnetic heads are arranged, and more particularly to an apparatus and a method for correcting a bend of the workpiece during the machining work. 
     2. Related Background Art 
     A thin film magnetic head to be used in a magnetic disc apparatus or the like is composed of parts obtained by machining a rod-shaped ceramic (hereinafter referred to as a ceramic bar) where a number of element parts made of a magnetic thin film or the like forming induction type magnetic converting elements, magnetic resistors (hereinafter referred to as MRs) elements or the like are formed in a line on a surface. Conventionally, in a batch type manufacturing process of parts for the thin film magnetic head, the ceramic bar where the plurality of element portions are formed is polished, and a process for machining a throat height or an MR height of each element part to a suitable level is executed. In general, in the magnetic disc apparatus, in order to stabilize the output characteristics from the magnetic head, it is necessary to keep a distance between the magnetic polar portions of the magnetic head and a surface of a recording medium to an extremely narrow constant distance. The value of the throat height or the like is used as an important parameter for defining this distance. 
     In the following description, the throat height means a length (height) of the tip end portion of the magnetic poles for performing the recording/reproduction of magnetic signals in such a head core part, i.e., the portion where the two magnetic poles face each other at a fine gap. Also, the MR height means a length (height) from the end portion of the MR element on the side facing the medium to the opposite end portion thereof. In order to make it possible to perform the suitable recording/reproduction of the signals, the values of the throat height, the MR height and the like must be selected suitably. In order to obtain the predetermined values, high precision is needed for the polishing work. 
     The ceramic bar is to be cut into respective element portions in a process thereafter. Each of the element portions constitutes a part of a magnetic head for the magnetic disc apparatus. In the case where the magnetic head is used in the magnetic disc apparatus, the ceramic portion becomes a slider that is to be lifted away from the magnetic disc by the blow pressure caused by the rotation of the disc. The element portion becomes a head core for performing the recording and/or reproducing the magnetic signals of the disc. 
     However, in general, the above-described ceramic bar has a strain, a bend or the like due to the stress caused by the formation of the element portion or the cutting operation from the ceramic substrate. It is therefore difficult to obtain the high machining precision only by fixing the ceramic bar and effecting the polishing work thereon. For this reason, a non-general polishing apparatus for performing the polishing work of the magnetic head with high precision in the form of the ceramic bar as disclosed in, for example, U.S. Pat. No. 5,620,356 or the like has been proposed. Also, the present assignee proposes some apparatus and some methods (Japanese Patent Application No. 11-162799 or the like). 
     An actual polishing method for the above-described ceramic bar will now be described. 
     First of all, the surface opposite the polishing surface of the ceramic bar, is fixed with adhesives or the like to a jig, and the surface to be polished of the ceramic bar is depressed through the jig against the polishing surface of a polishing base to perform the polishing work to the surface to be polished. The jig has a beam structure. A load is applied to several, three to seven, specific points on the jig from the outside of the jig to thereby cause deformation in the jig as a whole. Furthermore, this beam structure allows the portions fixed to the ceramic bar to be subjected to the complicated deformation by the balance adjustment of the above-described load, and the ceramic bar is bent simultaneously with the fixed portions to thereby make it possible to correct the bend or the like owned by the ceramic bar per se. 
     In the polishing work, in a predetermined element portion on the ceramic bar fixed to the jig, the values such as a throat height are measured optically or electrically to thereby obtain the difference between the measurement value and the target value, i.e., the amount of polished portion needed upon the measurement. The loads at the plurality of points are adjusted on the basis of the necessary polishing amount in the predetermined element portion obtained and the portion in the vicinity of the predetermined element portion, and the ceramic bar is polished while being deformed through the jig. These steps are repeated whereby the values such as the throat height and the like of all the elements formed in the ceramic bar fall within the predetermined range. 
     Opening portions into which pins or the like may be inserted are formed in the beam portion of the jig. The loads to the jig in the above-described process are given by transmitting the loads due to an actuator such as a low friction cylinder to the pins inserted into the opening portions of the jig through transmission parts. The adjustment of the loads to the jig is performed by adjusting the loads from this actuator, i.e., a drive amount of the actuator. Incidentally, Japanese Patent Application No. 10-178949 filed by the present applicant discloses a specific example of a jig for causing an effective deformation or a load distribution to the ceramic bar. 
     In a recording density in the current magnetic disc apparatus or the like, it is possible to make the values such as a throat height fall within an allowable range to some extent by a machining method of the magnetic head using the above-described jig. However, the high recording density is accelerated, and recently, the high precision of the throat height or the miniaturization of the elements are remarkable. It is difficult to make the values such as the throat height fall within the allowable range over the full length of the ceramic bar. 
     In the case where the allowable range of the values such as the throat height is narrowed, there is an approach to cope with this by, for example, increasing the application points of the loads that cause the deformation in the jig. However, since this leads to the increase of the number of the actuators that actually apply the loads or the transmission portions (application points) of the loads, if the actuators or the like used in the conventional apparatus are needed, it is difficult to actually perform this approach since the space for mounting the actuators or the like would be increased remarkably in view of the structure of the polishing apparatus. Also, in the case where the jig per se is miniaturized in accordance with the miniaturization of the elements, there would be a problem in that it is difficult to arrange the necessary number of the actuators or the like for applying the loads to the application points of necessary loads, and the like. 
     Furthermore, in the conventional polishing method, since the affect of the repulsive force from the polishing surface exists between the application point of the load and the beam or between the application points, it is impossible to sufficiently deform the ceramic bar. Accordingly, also in some conventional cases, depending upon the allowable range of the values such as a throat height, the values of the portion that may not be deformed could not fall within the allowable range. The approach to increase the number of the application points of the load and the number of the actuators for this problem has been attempted but there is a limit in the allowable range due to the above described problem. 
     Also, the conventional apparatus has three to seven actuators for deforming the jig in addition to the actuator for applying the main pressure for depressing the ceramic bar against the polishing surface and adjusting the load balance at both end portions in the longitudinal direction of the ceramic bar. However, actually, in order to bend the retainer portions to a necessary level, the three to seven actuators have to have a large stroke due to the necessary bend level and the actuators that always have the large stroke and occupy the large space in the structure are necessary as in the conventional case. Moreover, in order to make it possible to provide the complicated bend, the opening portion of the jig into which the pins cooperating with the actuators are inserted is increased to provide the form that may imparts a moment in the vertical direction, in the lateral direction and in the rotational direction with respect to the opening portion. In addition, it is necessary to effect the complicated drive control for each actuator. Accordingly, the conventional apparatus is not suitable for imparting the predetermined deformation amount to the very restricted portions of the ceramic bar. 
     SUMMARY OF THE INVENTION 
     In view of the above, an object of the present invention is to provide an apparatus that easily imparts a complicated bend deformation or the like to an object to be machined (polished) such as a ceramic bar by using an actuator having a small drive stroke in comparison with a conventional apparatus to make it possible to impart a depression force also to a specific portion whereby decreasing non-uniformity of a machining (polishing) amount of the object to be machined (polished) through the machining (polishing) process of the object to be machined (polished). 
     In order to solve this and other objects, according to the present invention, there is provided a machining apparatus for machining an object, elongated in one direction, to be machined, comprising: a machining base with a machining surface to be rotationally driven, a machining head mounted frame disposed movably to the machining surface, and a machining head supported by the machining head mounted frame, characterized in that the machining head includes a jig for holding the object to be machined, an up-and-down moving portion moving up and down relative to the machining surface together with the jig, and a correcting mechanism supported by the up-and-down moving portion, the correcting mechanism includes a base fixed to the up-and-down moving portion, a plurality of levers each of which has a pin at one end, a shaft fixed to the base for rotatably supporting the levers, and a plurality of correcting drive means coupled to other ends of the levers for pivoting the levers with respect to the shaft to thereby pivot the pins, the jig includes a body portion fixed to the up-and-down moving portion, a holding portion elongated in one direction and fixed to the body portion for holding the object to be machined, and a plurality of load receiving portions arranged in parallel in the one direction on the holding portion, and the load receiving portions receive the pins and are driven in accordance with the pivotal movement of each pin whereby portions corresponding to the load receiving portion in the holding portion are deformed together with the object to be machined. 
     Also, according to the present invention, it is preferable that tip ends of the pins are substantially spherical. It is preferable that the adjacent levers each have different lengths from each other, and distances between the plurality of correcting drive means and the shaft are different from each other in accordance with a length of the levers. Also, it is preferable that the shaft supports the levers in a position in the vicinity of the pins and the correcting drive means are REC plungers. 
     Furthermore, in order to attain the above-noted object, according to the present invention, there is provided a machining apparatus for machining an object, elongated in one direction, to be machined, comprising: a machining base with a machining surface to be rotationally driven, a machining head mounted frame disposed movably to the machining surface, and a machining head supported by the machining head mounted frame, characterized in that the machining head includes a jig for holding the object to be machined, an up-and-down moving portion moving up and down relative to the machining surface together with the jig, and a correcting mechanism supported by the up-and-down moving portion, the correcting mechanism includes a base fixed to the up-and-down moving portion, a plurality of correcting drive means each of which is fixed at an end to the base, a shaft coupled coaxially with the correcting drive means, and pins projecting from the shaft, the jig includes a body portion fixed to the up-and-down moving portion, a holding portion elongated in one direction and fixed to the body portion for holding the object to be machined, and a plurality of load receiving portions arranged in parallel to the one direction on the holding portion, and the load receiving portions receive the pins and are driven in accordance with the movement of each pin whereby portions corresponding to the load receiving portion in the holding portion are deformed together with the object to be machined. 
     Furthermore, in order to attain the above-noted object, according to the present invention, there is provided a machining apparatus for machining an object, elongated in one direction, to be machined, comprising: a machining base with a machining surface to be rotationally driven, a machining head mounted frame disposed movably to the machining surface, and a machining head supported by the machining head mounted frame, characterized in that the machining head includes a jig for holding the object to be machined, an up-and-down moving portion moving up and down relative to the machining surface together with the jig, and a correcting mechanism supported by the up-and-down moving portion, the correcting mechanism includes a base fixed to the up-and-down moving portion, a plurality of substantially frame-like members fixed to the base, a plurality of correcting drive means held on centerlines of the substantially frame-like members, and a plurality of shafts extending in parallel with a drive direction of the correcting drive means, coupled at first ends with the substantially frame-like members and provided at the other ends with pins, the jig includes a body portion fixed to the up-and-down moving portion, a holding portion elongated in one direction and fixed to the body portion for holding the object to be machined, and a plurality of load receiving portions arranged in parallel in the one direction on the holding portion, and the load receiving portions receive the pins and are driven in accordance with the movement of each pin whereby portions corresponding to the load receiving portion in the holding portion are deformed together with the object to be machined. 
     Also, according to the present invention, it is preferable that tip ends of the pins are substantially spherical and the adjacent shafts each have different lengths from each other, and distances between the correcting drive means and the pins are different from each other in accordance with a length of the shafts. Also, according to the present invention, it is preferable that the shafts are arranged coaxially with the correcting drive means and the correcting drive means are piezoelectric element actuators. 
     Furthermore, in order to attain the above-noted object, according to the present invention, there is provided a machining apparatus for machining an object, elongated in one direction, to be machined, comprising: a machining base with a machining surface to be rotationally driven, a machining head mounted frame disposed movably to the machining surface, and a machining head supported by the machining head mounted frame, characterized in that the machining head includes a jig for holding the object to be machined, an up-and-down moving portion moving up and down relative to the machining surface together with the jig, and a correcting mechanism supported by the up-and-down moving portion, the correcting mechanism includes a plurality of shafts provided at ends with pins and having convex portions different from the pins, a pair of correcting drive members disposed on one line on both sides of the convex portions and clamping the convex portions, and a base fixed to the up-and-down moving portion with recess portions receiving the pair of correcting drive member and the convex portions, the pair of correcting drive members drive the convex portion in a straight line to drive the shafts and the pins in parallel with the straight line, the jig includes a body portion fixed to the up-and-down moving portion, a holding portion elongated in one direction and fixed to the body portion for holding the object to be machined, and a plurality of load receiving portions arranged in parallel in the one direction on the holding portion, and the load receiving portions receive the pins and are driven in accordance with the movement of each pin whereby portions corresponding to the load receiving portion in the holding portion are deformed together with the object to be machined. 
     Also, according to the present invention, it is preferable that tip ends of the pins are substantially spherical and sizes of projections of the adjacent convex portions are different from each other and the arrangement of the correcting drive members each received in the recess portion and a size of the recess portions are defined in accordance with the sizes of the convex portions. Also, according to the present invention, it is preferable that the pair of correcting drive members have a pair of pistons to be driven by pressure medium, and the base has a pair of pressure medium introduction ports in communication with a rear portion of each of the pair of pistons and the pair of adjacent pressure medium introduction ports are each arranged at different distances from a predetermined surface of the base. 
     Also, according to the present invention, it is preferable that one of the pair of correcting drive members has a piston to be driven by pressure medium, the other being formed of elastic member, and the base has a pressure medium introduction port in communication with a rear portion of the piston. Also, it is preferable that the pair of adjacent pressure medium introduction ports are each arranged at different distances from a predetermined surface of the base. Also, it is preferable that the pressure medium is pressurized air. 
     Furthermore, in order to attain the above-noted object, according to the present invention, there is provided a machining apparatus for machining an object, elongated in one direction, to be machined, comprising: a machining base with a machining surface to be rotationally driven, a machining head mounted frame disposed movably to the machining surface, and a machining head supported by the machining head mounted frame, characterized in that the machining head includes a jig for holding the object to be machined, an up-and-down moving portion moving up and down relative to the machining surface together with the jig, and a correcting mechanism supported by the up-and-down moving portion, the correcting mechanism includes a shaft, a plurality of levers composed of linear portions provided at ends with pins and supported rotatably by the shaft at portions different from the pins and driven portions coupled at end portions with the linear portions having convex portions, a pair of correcting drive members disposed in a linear manner on both sides of the convex portions while clamping the convex portions, and a base having recess portions for receiving the pair of correcting drive members and the convex portions and fixed to the up-and-down moving portion, the pair of correcting drive members drive in the linear manner to thereby drive the convex portion clamped thereby, whereby the levers and the pins are pivoted about the shaft, the jig includes a body portion fixed to the up-and-down moving portion, a holding portion elongated in one direction and fixed to the body portion for holding the object to be machined, and a plurality of load receiving portions arranged in parallel in the one direction on the holding portion, and the load receiving portions receive the pins and are driven in accordance with the pivotal movement of each pin whereby portions corresponding to the load receiving portion in the holding portion are deformed together with the object to be machined. 
     Also, according to the present invention, it is preferable that tip ends of the pins are spherical and it is preferable that sizes of projections of the adjacent convex portions are different from each other and the arrangement of the correcting drive members each received in the recess portion and a size of the recess portion are defined in accordance with the sizes of the convex portions. It is also preferable that the pair of correcting drive members have a pair of pistons to be driven by pressure medium, and the base has a pair of pressure medium introduction ports in communication with a rear portion of each of the pair of pistons. It is preferable that the pair of adjacent pressure medium introduction ports are each arranged at different distances from a predetermined surface of the base. 
     Also, it is preferable that one of the pair of correcting drive members has a piston to be driven by pressure medium, the other being formed of elastic member and the base has a pressure medium introduction port in communication with a rear portion of the piston. Its preferable that the pair of adjacent pressure medium introduction ports are each arranged at different distances from a predetermined surface of the base. Also, it is preferable the pressure medium is pressurized air and tip end portions of the pistons are substantially spherical. 
     Furthermore, according to the present invention, it is preferable that the jig has an electrode to be connected to an electric element formed on the object to be machined, and the correcting mechanism has a probe unit to be brought into contact with the electrode. Also, according to the present invention, it is preferable that the machining head has a balancing actuator, the jig has through holes in a central portion and both end portions in the longitudinal direction of the body portion, the jig is supported by the correcting mechanism by a fixing pin passing through the through hole in the central portion, and the jig is depressed to a direction toward the machining surface through the positioning pins at both end portions by the balancing actuator. 
     Also, according to the present invention, it is preferable that the machining head is supported through an adjust ring supported by the machining head mounting frame and in contact with the machining surface, and an angle of the machining head supported by the machining head mounting frame facing the machining surface is defined by the adjust ring. Also, it is preferable that the machining head is mounted rotatably to rails for mounting the machining head. Furthermore, it is preferable that the apparatus according to the invention further comprises a machining head swinging means, in which the machining head swinging means performs reciprocating rotational motion of the machining head within a predetermined angular range. It is more preferable that the object to be machined is a rod-like ceramic provided with a plurality of magnetic heads. 
     Furthermore, in order to attain the above-noted object, according to the present invention, there is provided a method for machining an object, to be machined, elongated in one direction by holding the object to be machined to a jig, and depressing the object to be machined to a machining surface formed in a machining base that is rotationally driven, through the jig, comprising the steps of: measuring a machining amount at a plurality of positions of the object to be machined when the object to be machined is depressed against the machining surface; and rotating a plurality of levers having pins at ends, together with the pins by a plurality of correcting drive means on the basis of the measured machining amount for imparting a predetermined deformation to the object to be machined together with the jig by the rotation of the pins with tip ends received in the jig. 
     Furthermore, in order to attain the above-noted object, according to the present invention, there is provided a method for machining an object to be machined, elongated in one direction by holding the object to be machined to a jig, and depressing the object to be machined to a machining surface formed in a machining base that is rotationally driven, through the jig, comprising the steps of: measuring a machining amount of a plurality of positions of the object to be machined when the object to be machined is depressed against the machining surface; and driving a plurality of shafts, disposed on the same axes with a plurality of correcting drive means and having pins, on the basis of the measured machining amount for imparting a predetermined deformation to the object to be machined together with the jig by the drive along the axes of the pins with tip ends received in the jig. 
     Furthermore, in order to attain the above-noted object, according to the present invention, there is provided a method for machining an object to be machined, elongated in one direction by holding the object to be machined to a jig, and depressing the object to be machined to a machining surface formed in a machining base that is rotationally driven, through the jig, comprising the steps of: measuring a machining amount at a plurality of positions of the object to be machined when the object to be machined is depressed against the machining surface; and driving a plurality of shafts having pins linearly by a pair of correcting drive means disposed on a plurality of straight lines on the basis of the measured machining amount and imparting a predetermined deformation to the object to be machined together with the jig by the drive on the straight lines of the pins with tip ends received in the jig. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall frontal view showing a polishing apparatus of a magnetic head in accordance with an embodiment of the present invention. 
         FIG. 2  is an overall plan view showing the polishing apparatus of the magnetic head in accordance with the embodiment of the present invention. 
         FIG. 3  is frontal view showing a polishing head and the like in the polishing apparatus of the magnetic head shown in FIG.  1 . 
         FIG. 4  is a plan view showing the polishing head shown in FIG.  3 . 
         FIG. 5  is a side elevational view showing the polishing head shown in FIG.  3 . 
         FIG. 6  is a side elevational cross-sectional view showing the polishing head shown in FIG.  3 . 
         FIG. 7  is a bottom view showing an adjust ring usable in the polishing head according to the invention. 
         FIG. 8  is a plan view showing a correcting mechanism in accordance with a first embodiment of the invention. 
         FIG. 9  is a frontal view of the correcting mechanism shown in FIG.  8 . 
         FIG. 10  is a side elevational view of the correcting mechanism shown in FIG.  8 . 
         FIG. 11  is a schematic cross-sectional view taken along the line  11 — 11  of the correcting mechanism shown in FIG.  9 . 
         FIG. 12  is a frontal view of a polished object mounting jig used in the embodiment of the invention. 
         FIG. 13  is a block diagram in conjunction with a polishing amount control in accordance with the embodiment of the invention. 
         FIG. 14  is a diagram showing detail of the measurement and a multiplex substrate shown in FIG.  13 . 
         FIG. 15  is a view showing a detail of a micro actuator driving substrate shown in FIG.  13 . 
         FIG. 16  is a side elevational cross-sectional view of a polishing head according to a second embodiment of the invention. 
         FIG. 17  is a plan view of a correcting mechanism in accordance with the second embodiment of the present invention. 
         FIG. 18  is a frontal view of the correcting mechanism shown in FIG.  17 . 
         FIG. 19  is a schematic cross-sectional view taken along the line  19 — 19  of the correcting mechanism shown in FIG.  18 . 
         FIG. 20  is a side elevational cross-sectional view of a polishing head according to a third embodiment of the invention. 
         FIG. 21  is a plan view of a correcting mechanism in accordance with the third embodiment of the present invention. 
         FIG. 22  is a frontal view of the correcting mechanism shown in FIG.  21 . 
         FIG. 23  is a schematic cross-sectional view taken along the line  23 — 23  of the correcting mechanism shown in FIG.  22 . 
         FIG. 24  is a view showing a rear surface of the correcting mechanism where adjacent pressurized medium introduction ports are arranged in a staggered manner in the third embodiment. 
         FIG. 25  is a schematic cross-sectional view taken along the line  25 — 25  in the correcting mechanism shown in FIG.  24 . 
         FIG. 26  is a side elevational cross-sectional view of a polishing head according to a fourth embodiment of the invention. 
         FIG. 27  is a plan view of a correcting mechanism in accordance with the fourth embodiment of the present invention. 
         FIG. 28  is a frontal view of the correcting mechanism shown in FIG.  27 . 
         FIG. 29  is a schematic cross-sectional view taken along the line  29 — 29  of the correcting mechanism shown in FIG.  28 . 
         FIG. 30  is a view showing a rear surface of the correcting mechanism where adjacent pressurized medium introduction ports are arranged in a staggered manner in the fourth embodiment. 
         FIG. 31  is a schematic cross-sectional view taken along the line  31 — 31  in the correcting mechanism shown in FIG.  30 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     (First Embodiment) 
     A machining apparatus, i.e., a polishing apparatus of a magnetic head in accordance with a first embodiment of the present invention will now be described with reference to the accompanying drawings.  FIG. 1  is an overall frontal view showing the polishing apparatus of the magnetic head in accordance with the embodiment of the invention.  FIG. 2  is a plan view. The overall structure of the magnetic head polishing apparatus will now be described with reference to  FIGS. 1 and 2 . The magnetic head polishing apparatus is provided with a base  1 . A polishing base  2  which is a machining base is supported rotatably in a horizontal plane by the base  1 . Furthermore, the polishing base  2  is rotationally driven through a belt  6  by a base drive motor  4  that is a rotary drive source provided within the base  1 . 
     Also, a pair of guide rails  8  that are away from each other in the vertical direction are supported by the upper portion of the base  1  so as to extend in the horizontal direction. Furthermore, a lateral movement slider  10  is guided to be slidable in the horizontal direction by the pair of guide rails  8 . A polishing head mounted frame  12  that is a machining head mounted frame is mounted on the lateral movement slider  10  to be movable in the vertical direction (to be driven vertically for adjustment of the height level). The drive of the lateral movement slider  10  may be executed by, for example, threadedly engaging a ball screw nut on the slider  10  side with a ball screw shaft in parallel with the guide rails  8  and rotationally driving the ball screw shaft by a motor. Furthermore, the slider  10  and the polishing head mounting frame  12  may take a reciprocation linear motion. 
     As shown in  FIG. 3 , a rotary support portion  16  is rotatably supported through an annular bearing portion  14  inside of the polishing head mounting frame  12 . A polishing head  20  that is the machining head is mounted on the rotary support portion  16  through a coupling member  18  that is a rigid member. The polishing head  20  has a bottom plate  22  and a vertical support plate  24  fixed and implanted vertically in parallel with each other on the bottom plate  22 . As shown in  FIGS. 2 and 3 , a belt wheel (pulley)  28  is fixed to the rotary support portion  16 . A polishing head swinging motor  32  for rotationally driving a belt wheel (pulley)  30  is mounted outside of the polishing head mounting frame  12 . A belt  34  is laid around the belt wheels  28  and  30 . The motor  32 , the belt wheels  28  and  30  and the belt  34  function as a swing means for performing reciprocating rotational motion (swing motion) to the polishing head  20  within a predetermined angular range. 
     Incidentally, in this embodiment, a rigid member is used as the coupling member  18  and may hold the polishing head  20  stably substantially in the vertical direction to a polishing surface  2 a. However, in the case where it is difficult to ensure the polishing head  20  in a stable posture to the polishing surface  2 a in a polishing step, it is possible to use an elastic member such as a spring or a rubber as the coupling member and to further use an adjust ring for the purpose of stabilizing the posture of the head. 
     In this case, the adjust ring (wear pad)  26  is fixed to the bottom surface of the bottom plate  22  of the polishing head  20  and is disposed in contact with the polishing surface  2 a that is the top surface of the polishing base  2 .  FIG. 7  is a bottom view showing an example of the adjust ring. As shown in  FIG. 7 , the adjust ring  26  is one obtained by, for example, embedding a number of cylindrical dummies  38  made of wear-resistive ceramic in an aluminum made ring body  36 . The lower end faces of the cylindrical dummies  38  somewhat project from the ring body  36 . The number of the cylindrical dummies  38  is selected in conformity with the weight balance of the polishing head  20  to be laid on the adjust ring  26 . In the case of the adjust ring  26  shown in  FIG. 7 , since an arcuate portion  40  out of the arcuate portions  40  and  42  of the adjust ring  26  in contact with the polishing base  2  is subjected to more load of the polishing head  20 , the number of the cylindrical dummies  38  is increased therefor. 
     As shown in  FIGS. 3  to  6 , a slantable shaft  44  in parallel with a lower surface of the polishing base  2  is provided between the portions of the vertical support plate  24  of the polishing head  20 . A slantable portion  46  slantable to the polishing head  20  is pivoted about the slantable shaft  44 . 
     As shown in  FIGS. 5 and 6 , a lower portion of a motor mounting seat portion  48  is mounted rotatably at a pivot shaft  50  in the vertical support plate  24  of the polishing head  20 . A slanting motor  52  is fixed to an upper portion of the motor mounting seat portion  48 . A ball screw shaft  54  is coupled to a rotary drive shaft of the motor  52 . A ball screw nut  56  is engaged with this ball screw shaft  54 . One end of an arm  58  that is connected at the other end to the slantable portion  46  is coupled at a pivot shaft  60  to the ball screw nut  56 . The mechanism from the pivot shaft  50  to the pivot shaft  60  constitutes a slantable portion driving means for slanting the slantable portion  46  at a predetermined angle from the vertical plane to the polishing surface  2 a of the polishing base  2 . 
     An up-and-down moving portion  64  is mounted to be movable up and down to the slantable portion  46  through a slide bearing (cross roller guide)  62  in the slantable portion  46 . It should be noted that, since the movement of the up-and-down moving portion  64  is performed together with the slantable portion  46 , the slantable portion  46  and the up-and-down moving portion  64  are always kept in a parallel condition. A back plate  68  is pivoted at a pivot shaft  66  perpendicular to the slantable shaft  44  and in parallel with the lower surface of the polishing base  2 . 
     As shown in  FIGS. 3 and 5 , balancing actuators  70 A and  70 B are mounted through a bracket  72  on an upper portion of the slantable portion  46 . These balancing actuators  70 A and  70 B are used for lifting upwardly right and left sides of a pivot shaft (a central portion in the longitudinal direction) of the back plate  68  (application of drawing pressure) and for controlling the load applied to the back plate  68 . 
     The balancing actuators  70 A and  70 B shown in this embodiment are electromagnetic REC plungers and are composed of frames  74 A and  74 B, coils  76 A and  76 B mounted inside the frames  74 a and  74 B to form the stationary portions, magnets  78 A and  78 B mounted on central portions of the actuators  70 A and  70 B to form movable portions and rods  80 A and  80 B mounted integrally with the centers of the magnets  78 A and  78 B. Up-and-down moving members  82 A and  82 B each having an L-shaped cross section are connected to be movable up and down along slide bearing  84 A and  84 B mounted on the frames  74 A and  74 B at the lower ends of the rods  80 A and  80 B. The lower end sides of the up-and-down moving members  82 A and  82 B and the right side and left side of the back plate  68  are coupled with each other through coupling links  88 A and  88 B. Here it should be noted that the moving direction of the magnets  78 A and  78 B and a direction in which a force is applied to the back plate  68  are parallel with each other. 
     In the actual polishing work, the adjustment of the main depressing load to the polishing surface  2 a of an object  92  to be polished is performed by the balancing actuators  70 A and  70 B. Simultaneously, the adjustment of the rough balance of the depressing load in the longitudinal direction of the object  92  to be polished is performed. In this embodiment, more specifically, a force for drawing the object  92  to be polished mainly upwardly (drawing force) is applied to the actuators  70 A and  70 B in response to the change in magnitude of the polishing amount and the portion to be polished in the longitudinal direction of the object  92  to be polished. However, it is possible to partially apply the depressing force (force in the direction the object  92  to be polished is depressed against the polishing surface) in response to the necessary polishing amount of each portion. 
     A correcting mechanism  100  for actually correcting the bend or the like of the object  92  to be polished through a jig  94  upon the polishing work is fixed to the back plate  68  and the correcting mechanism  100  per se is driven by the balancing actuators  70 A and  70 B. Hereafter, the correcting mechanism  100  will be described in detail. 
       FIGS. 8 ,  9  and  10  are a plan view, a frontal view and a side elevational view of the correcting mechanism  100  in accordance with this embodiment, respectively. A base  101  is fixed substantially in parallel with the back plate  68  by means of screws or the like so that the correcting mechanism  100  per se is fixed to the back plate  68 . A bracket  103  is fixed through a holder  102  at an upper portion of the base  101 . Both side surfaces of the bracket  103  are arranged substantially in parallel with the back plate  68 . Plates  104  and  105  are fixed in parallel on both side surfaces of the bracket  103 . The bracket  103  is clamped between these two plates so that a correcting actuator  106  composed of a plurality of correcting drive means is held in a predetermined position. 
       FIG. 11  is a side elevational view showing the structure of the drive portion of the correcting mechanism  100 . As shown in  FIG. 11 , each correcting actuator  106 , at the driving portion thereof, is connected to one end of a lever  113  extending substantially perpendicular to the drive direction through a joint  118  and a pin  117 . Furthermore, the lever  113  is rotatably supported through a bearing  112  by a shaft  111  fixed to the base  101  and is rotated about the shaft  111  by the drive of the correcting actuator  106 . The lever  113  is provided with a pin  113 a at the other end of the coupling portion with the driving portion so as to be rotated about the shaft  111 . 
     In the embodiment, the shaft  111  is provided in the vicinity of the pin  113 a for supporting the lever  113  whereby the drive force obtained from the correcting actuator  106  is amplified due to the lever principle and the fine control to the pin  113 a may be performed. The tip end of the pin  113 a is machined in a spherical shape and is driven in a direction that is substantially perpendicular to the driving direction of the actuator (substantially in the vertical direction of the polishing surface  2 a) by the drive of the correcting actuator  106 . 
     Incidentally, since the interval of the adjacent pins  113 a is smaller than the size (diameter in this case) of the correcting actuators  106  used in this embodiment, it is impossible to simply arrange the correcting actuators  106  in parallel with each other. Therefore, as shown in  FIG. 11 , the length of the lever  113  is changed in each case so that the correcting actuators  106  are arranged in a staggered manner to provide the retainer space for the correcting actuators  106 . In this case, the drive amounts of the tip ends of the pins  113 a are different from each other due to the difference in length of the levers  113 . However, according to this embodiment, the respective drive strokes of the correcting actuators  106  are limited to a predetermined range, and simultaneously therewith, the count numbers for measuring the actual drive amounts of the pins  113 a are made different from each other to thereby keep constant the drive amounts of the tip ends. 
     As shown in  FIGS. 6  or  9 , a pair of positioning pins  107 a and a fixing pin  107  projecting in a direction opposite the back plate  68  are fixed in parallel with each other at both end portions and the central portion in the longitudinal direction in the lower portion of the base  101 . A bracket  108  having probe units  109  and  110  composed of a plurality of resistor measuring terminals  128  or the like is fixed by using the pair of positioning pins  107 a. The jig  94  for holding the object  92  to be polished is held so as to clamp the bracket  108  to the base  101  by using both the fixing pin  107  and the positioning pins  107 a. 
     As shown in a frontal view of  FIG. 12 , for example, the jig  94  is formed in an integral frame shape composed of a body portion  131  elongated in one direction, a holding portion  132  having substantially the same length as that of the body portion  131  disposed in parallel with the body portion  131  and joint portions  133  and  134  for coupling the body portion  131  and the holding portion  132  at both end portions in the longitudinal direction. Holes  120 a and  120  through which the positioning pins  107 a and the fixing pin  107  pass are provided in the body portion  131 , and the body portion  131  is fixed to the base  101 . In the holding portion  132 , a plurality of load receiving portions  145  are arranged in the longitudinal direction on the portion of the inside of the frame and holding portion  132  holds the object  92  to be polished on the portion of the outside of the frame. 
     A load receiving hole  146  is formed in a central portion of each load receiving portion  145 . When the jig  94  is fixed to the base  101 , a spherical portion at the tip end of the pin  113 a is inserted into the load receiving hole  146 . In accordance with the drive of the correcting actuator  106 , the tip end portion of the pin  113 a depresses the peripheral portion of the load receiving hole  146  to drive the load receiving portion  145  up and down. In accordance with the movement of this load receiving portion  145 , the holding portion  132  is partially deformed and simultaneously, the portion  92  to be polished is locally deformed. 
     Incidentally, the tip end portion of the pin  113 a is not moved up and down in a linear manner but is moved up and down while depicting an arcuate locus in accordance with the arcuate rotation of the lever  113  about shaft  111 . For this reason, in the embodiment, the tip end portion is made spherical so that the tip end portion may slide to the peripheral portion of the load receiving hole  146  to enable the smooth slide of the load receiving portion  145  with respect to the tip end portion. 
     In the object  92  to be polished to be fixed to the holding portion body  132 , element portions of a number of magnetic heads made of magnetic thin film pattern are arranged in a single line on the elongated rectangular ceramic bar (to be divided into elements for sliders of the thin film magnetic head). The magnetic thin film pattern of these element portions is arranged on one side longitudinal surface of the ceramic bar. Accordingly, the bottom surface of the ceramic bar is polished so that the throat height and the MR height may be reduced in the element portion formed on the above-described longitudinal side surface. 
     As described above, the strain, the distortion or the like is present in the object  92  to be polished. When the object  92  is to be polished, it is necessary to polish it after correcting the strain or the like. In this embodiment, the amount of bend deformation that is needed in each position in the longitudinal direction of the object  92  to be polished is corrected by driving up and down each load receiving portion  145  formed in the lateral longitudinal jig  94  by the necessary amount. 
     Accordingly, upon the polishing work, it is necessary to seek the necessary drive amount of the loading receiving portion  145 , i.e., the amount of bend deformation of the object  92  to be polished. A specific example for seeking the necessary amount of deformation during polishing work and driving the correcting actuator  106  on the basis of the sought value will now be described. In the embodiment, additional electrodes are provided on the longitudinal side surface of the ceramic bar in addition to the elements. The additional electrodes reduce the size of the ceramic bar in accordance with the polishing work of the ceramic bar and increase the resistance value. In the embodiment of the invention, the polishing work according to a so-called closed loop control in which the change of the resistance value of the additional electrodes is monitored and the polishing amount at the monitoring time is sought to thereby seek the further necessary amount of deformation on the basis of the obtained polishing amount is performed to control the polishing amount in the object  92  to be polished. 
     For this reason, the electrodes electrically connected to the additional electrodes by wire bonding are formed in advance on a surface, on the confronting side to the bracket  108 , of the lateral longitudinal jig  94 . Measurement pins  128  biased by spring or the like are implanted in the probe units  109  and  110  on the bracket  108 . When the lateral longitudinal jig  94  is fixed to the base  101 , the above-described electrodes and the measurement pins  128  are bought into contact with each other. Furthermore, the measurement pins  128  are connected to the resistance value measurement means (not shown), and the lateral longitudinal jig  94  is fixed to the base  101  to thereby make it possible to measure the resistance value of the additional electrodes. 
     The structure of the specific resistance value measurement means and the control means of the actuator  106  will now be described.  FIG. 13  is a control block diagram for driving the correcting actuator  106  on the basis of the resistance value of the measured additional electrodes including the above-described measurement means and control means.  FIG. 14  is a detailed block diagram of a measurement and multiplex substrate  220 .  FIG. 15  is a detailed block diagram of the actuator drive substrate. Incidentally, in the embodiment, since the resistance value is measured in accordance with a four-terminal method, a plurality of measurement pins  128  are brought into contact with a single additional electrode  201 . 
     The voltage obtained by the additional electrode  201  through the measurement pins  128  with the measurement and multiplex substrate  220  is converted into resistance values on the basis of the calculation used in a well known four-terminal measurement. Furthermore, these values are converted and multiplexed as digital data and inputted into an input/output terminal  211  of a microcomputer  210 . Furthermore, using the data inputted in the computer  210 , the polishing amount of the object  92  to be polished is calculated to display the polishing amount to the operator. 
     The above-described signal processing from the measurement of the resistance values to the output of the digital data will now be described in detail with reference to FIG.  13 . In the measurement and multiplex substrate  220 , the supply of current from a constant current power source  221  to the plurality of measurement pins  128 , the measurement of voltage between the respective pins, and, in a calculation portion  223 , the numerical calculation on the basis of the comparison of the value of a correcting resistance  222  with the measurement value are continuously performed to obtain the resistance value of the additional electrode. The obtained value is converted into digital data by an A/D converter  224 . 
     The necessary polishing amount of the portion where the measured additional electrode on a surface  92 a to be polished and the amount of vicinity thereof is formed and sought. Subsequently, in order to perform the polishing work with the necessary amount, the drive amount needed for each load receiving portion  145  is sought as drive amount data in the computer  210 . The drive amount data is inputted into an actuator drive substrate  230  through the input terminal  211  from the computer  210 . 
     The data is converted into a contact signal in the actuator drive substrate  230 . The drive current is outputted to each correcting actuator  106  from a drive current output device  232  that has received the control signal. In response to the output, each correcting actuator  106  finely adjusts the amount of deformation given to the object  92  to be polished by the drive of the load receiving portion  145  of the lateral longitudinal jig  94  to thereby finely adjust the load balance of the polishing amount of the object  92  in each position in the longitudinal direction with respect to the polishing surface  2 a. 
     As described above, the correcting substrate  106  is controlled through the closed loop so that the object may be polished while monitoring the polishing amount to cope with the case where the allowable range of the non-uniformity of the polishing amount becomes narrower. Incidentally, it is possible to seek the polishing amount from the resistance of the actual elements, for example, the MR value without using the additional electrode. 
     The operation of the actual apparatus and the polishing method in accordance with the embodiment of this invention will now be described. First of all, in a position where the polishing head  20  shown in  FIGS. 1 and 2  is out of the polishing base  2 , the lateral longitudinal jig  94  holding the object  92  to be polished where a plurality of elements for the thin film magnetic heads are arranged is fixed to the base  101  by using the fixing pin  107  and the positioning pins  107 a. At that time, the additional electrode and electrodes provided on the side surface  94 a of the lateral longitudinal jig  94  have already been wire bonded and the measurement pin  128  is brought into contact with the above-described electrode. 
     All the tip end portion of the pin  113 a of each lever  113  is inserted into the load receiving hole  146  of the jig  94 . Thereafter, the slant angle of the back plate  68  with respect to the polishing head  20  is set at zero in the initial stage (in the case where the adjust ring is used, in a vertical position to the bottom surface of the adjust ring  26 , i.e., the vertical posture to the polishing base  2 ). 
     Here, depending upon the structure of the object to be polished, in the case where, for example, the elements and the like are built in the arrangement on the object to be polished that needs a very large polishing amount to obtain a predetermined throat height, there are some cases where a rough polishing work is performed in advance by another apparatus before the above-described mounting work. In this embodiment, in this case, this rough polishing is not performed under the condition that the object  92  to be polished is held in the lateral longitudinal jig  94  but the rough polishing is performed under the condition that the object  92  to be polished is fixed to another jig (not shown). However, the rough polishing may be performed by using the lateral longitudinal jig  94 . After the completion of the rough polishing, the object  92  to be polished is removed away from the another jig and is again fixed to the lateral longitudinal jig  94 . 
     After the mounting work of the lateral longitudinal jig  94  and the slant angle setting of the back plate  68 , the polishing head mounting frame  12  on which the polishing head  20  is mounted is moved in a linear manner along the guide rails  8  and positioned above the polishing base  2  that is rotationally driven. Furthermore, in order to bring the object  92  to be polished into contact with the polishing surface  2 a on the top surface of the polishing base  2 , the polishing head mounting frame  12  is lowered. When the adjust ring  26  is used, the polishing head mounting frame  12  is lowered so that a part of the lower surface of the plurality of cylindrical dummies  38  embedded in the lower surface thereof is brought into contact with the polishing surface  2 a of the top surface of the polishing base  2  and the part is kept in contact therewith at a suitable pressure. 
     Furthermore, the balancing actuators  70 A and  70 B are driven so that each parallel pressure force applied to the left side and the right side of the back plate  68  is adjusted and the object  92  to be polished is kept under the condition that object  92  to be polished is depressed substantially in parallel and against to the polishing surface  2 a. In this embodiment, the main pressure is obtained from the balancing actuators  70 A and  70 B. However, in this stage, the pressure to such an extent that the back plate  68  is supported is applied so as to keep the right and left balancing actuators  70 A and  70 B under the condition that both end portions of the object  92  to be polished is in contact with the polishing surface  2 a. Incidentally, this adjustment may be performed by visual observation or may be performed by using a contact sensor or the like. Also, it is possible to roughly measure, in advance, the bend of the object  92  to be polished and to adjust the balance of the pressure by the balancing actuators  70 A and  70 B so as to correct the bend in response to the measurement result. 
     Under this condition, the polishing of the object  92  to be polished is executed. The measurement of the polishing amount in accordance with the resistance value measurement of the additional electrode is performed at each desired timing to obtain the necessary polishing amount in each additional electrode formation position at a desired interval in the polishing step. Each correcting actuator  106 , i.e., the drive amount of the load receiving portion  145  is controlled in response to the obtained necessary polishing amount to make it possible to obtain the desired throat height or the like. Incidentally, in the case where the bend of the object to be polished is remarkable and simple like an arcuate shape and the distribution of the necessary polishing amount is remarkable, it is preferable to first perform the adjustment of the balance of the deformation amount by the balancing actuators  70 A and  70 B and thereafter to perform the drive amount adjustment of the correcting actuators. 
     Incidentally, in the case where the adjust ring is used, since, during the polishing step, the local wear is likely to occur if the same place of the adjust ring  26  is in contact with the polishing base  2 , the rotary support portion  16  on which the polishing head  20  and the adjust ring  26  are mounted is reciprocatingly rotated within a predetermined angular range by the polishing head swinging motor  32 , and the polishing head mounting frame  12  is reciprocatingly moved in a linear manner in a predetermined range. Accordingly, during the polishing step, the polishing head  20  and the adjust ring  26  take the composite motion of the reciprocating rotational motion and the reciprocating linear motion. 
     According to the above-described method, the bend of the ceramic bar that is the object to be polished may be corrected in more detail and may be polished so that the values of the throat height or the like may fall within the allowable range over the full length of the ceramic bar. 
     Incidentally, in this embodiment, the polishing head having the REC plungers as the balancing actuators  70 A and  70 B is used. However, the balancing actuators are not limited thereto or thereby, and it is possible to use a variety of kinds of low frictional cylinder such as an electromagnetic one. Also, in this embodiment, two actuators are used to compensate for the insufficiency of the drive stroke of the correcting actuators  106 . However, in order to more effectively compensate for the drive stroke of the correcting actuators, it is possible to increase the number of the balancing actuators. Also, in this case where the drive stroke of the correcting actuator  106  per se is sufficiently large, it is possible to dispense with the balancing actuators and to take the structure that has only the single drawing or depressing actuator. 
     Furthermore, in this embodiment, the REC plungers are used as the correcting actuators. However, the application of the present invention is not limited to this embodiment. It is possible to take a structure that has a pneumatic or electromagnetic cylinder or the like. Also, in this embodiment, the shaft  111  supports the levers  113  in the vicinity of the pins  113 a. The application of the invention is not limited to this embodiment. It is possible take a variety of arrangements such as the arrangement where the shaft is located, for example, in the vicinity of the correcting actuators  106  in view of the drive stroke and the drive load of the correcting actuators  106  and the pins  113 a. Also, the mounting position of the correcting actuators  106  to the plates  104  and  105  and the length of the levers  113  are not limited to those shown in this embodiment. It is preferable that these factors are selected in accordance with the size of the actuators  106  and the interval of the adjacent pins  113 a. 
     Also, the control in accordance with the closed loop of the embodiment is performed only by means of each correcting of micro actuator. However, in some possible cases, the necessary polishing amount obtained exceeds the drive range of the micro actuator, for example. For these cases, in the case where the obtained necessary polishing amount is greater than a predetermined value, the bend correction of the object to be polished only by the balancing actuators  70 A and  70 B at one end is performed and the operation goes into the subroutine for reducing the necessary polishing amount at first. It is possible to take the structure for performing the micro actuator in accordance with the closed loop thereafter. 
     Also, in this embodiment, the fixture of the object  92  to be polished to the lateral longitudinal jig  94  or the transfer jig, and the fixture of the transfer jig to the lateral longitudinal jig  94  are performed by thermoplastic adhesives. However, this invention is not limited thereto. It is possible to adopt the fixture with thermosetting or any other kind of adhesives, viscous material made of resin or the like, electrostatic adhesion, vacuum suction or the like. 
     Also, in the foregoing embodiment, only the polishing work has been described. It is obvious for those skilled in the art to apply the present invention not only to the polishing work but also the grinding work or any other suitable work. Furthermore, the present invention is not limited to the specific manners in the foregoing embodiment but it is possible for those skilled artisan to variously modify or change the invention within the scope of the appended claims. 
     (Second Embodiment) 
     A polishing apparatus for a magnetic head in accordance with a second embodiment of this invention will now be described with reference to the accompanying drawings. Incidentally, since the difference between the first embodiment and the second embodiment is only the structure of the bend correcting mechanism  100  and the bend correcting mechanism  200 , the duplicated description as to the portions except for the correcting mechanisms  100  and  200 , the control blocks for detecting the necessary polishing amount of the object  92  to be polished or the like in the overall structure of the apparatus will be omitted. The correcting mechanism  200  in accordance with the second embodiment of this invention will now be described in detail. 
       FIG. 16  is a side elevational view of the polishing head according to this embodiment.  FIGS. 17 ,  18  and  19  are a plan view, a frontal view and a side elevational view of the correcting mechanism  200  in accordance with this embodiment, respectively. The correcting mechanism  200  in accordance with this embodiment is composed of a base  150 , a holder  151 , an actuator holder  152  that is a frame-like member, a correcting actuator  153  that is a correcting drive means, a fixing pin  154 , positioning pins  154 a, a guide bracket  155 , shafts  156  and pins  157 . The base  150  is fixed substantially in parallel to the back plate  68  by fastening means such as screws. With this means, the correcting mechanism  200  per se is fixed to the back plate  68 . 
     The holder  151  is fixed to the upper portion of the base  150 . The holder  151  holds a plurality of actuator blocks  152  substantially in parallel to the back plate  68 . Each actuator holder  152  has the frame-like shape. The actuator holder  152  holds the correcting actuator  153  so as to be drivable in the same direction as the drive direction of the balancing actuators  70 A and  70 B. The actuator holder  152  is made of material that may be flexed and is driven to expand or contract in the drive direction of the correcting actuator in response to the expansion or contraction of the correcting actuator  152 . The actuator holder  152  is fixed to the holder  151  substantially immediately above the correcting actuator  153 , and holds one end of the shaft  156  extending in the drive direction of the correcting actuator  153  substantially immediately below the correcting actuator. 
     The fixing pin  154  for fixing the jig  94  holding the guide bracket  155  and the object  92  to be polished and the positioning pins  154 a for defining the fixture position are fixed to the lower portion of the base  150 . The above-described shaft  156  passes through each guide hole  155 a provided in the guide bracket  155 . Thus, the vertical drive of the shaft  156  in accordance with the correcting actuator  153  is prevented from being displaced out of the drive direction by the guide hole  155 a. Each pin  157  extending in the opposite direction to the base  150  is provided at the other end of the shaft  156 . In this embodiment, the tip end of the pin  157  is machined into a spherical shape. The tip end is driven in a direction substantially in parallel with the drive direction of the actuator (substantially perpendicular to the polishing surface  2 a) by the drive of the correcting actuator  153 . 
     As shown by dotted lines in  FIG. 19 , the jig  94  holding the object  92  to be polished positions so as to clamp the bracket  155  by the base  150  and the jig  94  by using the positioning pins  154 a and is fixed and held by using the fixing pin  154 . Incidentally, in this embodiment, since it is impossible to obtain the sufficient number of the contact points to the resistance measurement terminals  128  due to the work for the guide holes  155 a or the like, the probe units  109  and  110  made of a plurality of resistance measurement terminals  128  or the like are not provided directly to the guide bracket  155 . For this reason, unlike the first embodiment, the probe units  109  and  110  are discrete units from the guide brackets  155  that may be removed. The guide bracket  155  is fixed by using the fixing pin  154  to the opposite surface to the facing surface of the guide bracket  155  of the jig  94 . 
     It is possible to use the jig  94  as exemplified in the first embodiment except that the surface thereof where the electrodes electrically connected to the additional electrode by wire bonding is formed in advance, is the opposite surface to the facing surface of the guide bracket  155 . Namely, when the jig  94  is fixed to the base  150 , the spherical portion at the tip end of the pin  157  is inserted into the load receiving hole  146 . According to the drive of the correcting actuator  153 , the tip end portion of the pin  157  depresses the circumferential portion of the load receiving hole  146  to drive the loading receiving portion  145  up and down. The movement of the load receiving portion  145  deforms partially the holding portion  132  and simultaneously gives a local deformation also to the object  92  to be polished. 
     Incidentally, since the interval between the tip end portions of the adjacent pins  157  is large in comparison with the size of the correcting actuator  153  used in this embodiment (in this case, the cross-sectional area in the direction perpendicular to the expansion/contraction drive direction), it is possible to arrange simply the correcting actuators  153  in parallel with each other. However, in the case where it is necessary to reduce the interval between the pin tip end portions in comparison with the size of the correcting actuators  153 , it is possible to arrange the respective correcting actuators  153  in a staggered manner and to provide a holding space for each correcting actuator  153 . 
     Also, in this embodiment, each actuator holder  152  has the frame-like shape (frame). The correcting actuator  153  and the shaft  156  are arranged on a centerline thereof, and are held on the centerline to the holder  151 . However, the arrangement of the present invention is not limited thereto. If the rigidity of the correcting actuator may be compensated for, it is possible to take a variety of shapes such as a U-shape, for example, for the shape of the actuator holder. Furthermore, in the case where the rigidity of the correcting actuator per se is high, it is possible to take a structure for removing the actuator holder. Also, in the foregoing embodiment, it is possible to displace the pins in view of the moment to be applied to the tip end of each pin or the like. 
     Also, in the embodiment, a piezoelectric actuator is used as the correcting actuator  153 . However, the correcting actuator is not limited thereto. Also with respect to the arrangement of the probe units  109  and  110 , it is possible to take the same arrangement as that of the first embodiment in response to the number of the contact points with the available resistance measurement terminal  128 . Furthermore, the modifications or the like of each structure described in conjunction with the mode of the first embodiment such as the modification of the structure of the balancing actuators may be applied to this embodiment in the same manner. 
     (Third Embodiment) 
     In the second embodiment, the tip end portion of each pin  157  is moved up and down in a linear manner in response to the deformation of the correcting actuator  153 . For this reason, in the second embodiment, the drive amount of the correcting actuator  153  is small in comparison with the first embodiment, and, in addition, the piezoelectric element is used as each actuator so that a large deformation force may be given to the holder  152  with high precision, advantageously. However, since the piezoelectric elements that have a relatively small amount of deformation are used, there is a fear that the deformation amount to be given would be insufficient. Therefore, in accordance with the third embodiment, air cylinders are used as the correcting actuators. 
     A polishing apparatus for a magnetic head in accordance with a third embodiment of this invention will now be described with reference to the accompanying drawings. Incidentally, since the difference between the first embodiment and the third embodiment is the structure of the bend correcting mechanism  100  and the bend correcting mechanism  300 , the duplicated description as to the portions except for the correcting mechanism  300 , the control blocks for detecting the necessary polishing amount of the object  92  to be polished or the like in the overall structure of the apparatus will be omitted. The correcting mechanism  300  in accordance with the third embodiment of this invention will now be described in detail. 
       FIG. 20  is a side elevational view of the polishing head according to this embodiment.  FIGS. 21 ,  22  and  23  are a plan view, a frontal view and a cross-sectional view taken along the line  23 — 23  of  FIG. 22 , respectively. The correcting mechanism  300  in accordance with this embodiment is composed of a base  301 , cylinder syringes  302 ,  303 , piston  304 ,  305 , a guide bracket  306 , a fixing pin  307 , positioning pins  307 a and shaft  308 . 
     The base  301  is fixed substantially in parallel to the back plate  68  to only the upper portion by means of screws or the like to thereby fix the correcting mechanism  300  per se to the back plate  68 . A recess portion  321  that is composed of a top surface  321 a, a bottom surface  321 b and a vertical surface  321 c is formed on the surface opposite (hereinafter referred to as top surface) to the back plate  68  side in the lower portion of the base  301 . Also, pressurized gas introduction ports  323 ,  324  that are pressure medium introduction ports are provided on the surface on the back plate side (hereinafter referred as rear side surface). The pressurized gas introduced through the ports is introduced into the recess portion  321  from the top surface  321 a and the bottom surface  321 b through gas passages  325  and  326  that are medium flow paths formed in the interior of the base  301 . 
     Namely, in this embodiment, the correcting drive member is constituted by the pistons driven by the pressurized gas and the cylinder syringes for receiving the pistons and the correcting drive means is constituted by a pair of correcting drive members. 
     A guide groove is provided in the drive direction (hereinafter referred to as vertical direction) of the balancing actuators  70 A and  70 B in the guide bracket  306 . The surface side where guide groove is formed is faced to the top surface side of the base  301  so that the shaft  308  is held slidable in the vertical direction in the guide groove. The shaft  308  has a convex portion  308 a received in the recess portion  321  and a pin  308 b projecting in a direction different from the vertical direction in the lower portion in the vertical direction. The recess portions  321  further receives the pistons  304  and  305  in contact with the convex portion  308 a at upper surface and downward surface thereof in the vertical direction and the cylinder syringes  302  and  303  for receiving the pistons  304  and  305  slidably in the vertical direction, respectively. 
     For instance, in the case where the pressurized gas is introduced into the pressurized air introduction port  323 , the pressurized air that reaches the top surface  321 a through the gas flow path  325  drives the piston  304  within the cylinder syringe  302  downwardly in the vertical direction. The piston  305  is also in contact with the convex portion  308 a of the shaft  308 . However, in this case, since the force of the piston  304  for driving downwardly the convex portion  308 a is stronger, the shaft  308  and the pin  308 b are driven downwardly. Also, in the case where the shaft  308  and the pin  308 b are to be driven upwardly, it is sufficient to introduce the pressurized gas into the pressurized gas introduction port  324 . It is possible to adjust the drive amount of the shaft  308  and the pin  308 b by the adjustment of the pressure balance of the gas to be introduced to the port  323  and the port  324 . 
     As shown by dotted lines in  FIG. 23 , the jig  94  holding the object  92  to be polished positions so as to clamp guide bracket  306  by the base  301  and the jig  94  by using the positioning pins  307 a, and is fixed and held by using the fixing pin  307 . Incidentally, in this embodiment, since it is impossible to obtain the sufficient number of the contact points to the resistance measurement terminals  128  due to the work for the guide groove or the like, the probe units  109  and  110  made of a plurality of resistance measurement terminals  128  or the like are not provided directly to the guide bracket  306 . For this reason, unlike the first embodiment, the probe units  109  and  110  are discrete units from the guide bracket  306  that may be removed. The guide bracket  306  is fixed by using the fixing pin  307  to the opposite surface of the facing surface to the guide bracket  306  of the jig  94 . 
     It is possible to use the jig  94  as exemplified in the first embodiment except that the surface thereof where the electrodes electrically connected to the additional electrode by wire bonding is formed in advance is the opposite surface to the facing surface, of the guide bracket  307 . Namely, when the jig  94  is fixed to the base  301 , the spherical portion at the tip end of the pin  308 b is inserted into the load receiving hole  146 . According to the drive of the pistons  304  and  305 , the tip end of the pin  308 b depresses the circumferential portion of the load receiving hole  146  to drive the loading receiving portion  145  up and down. The movement of the load receiving portion  145  deforms locally the holding portion  132  and simultaneously gives a local deformation also to the object  92  to be polished. 
     Incidentally, since the interval between the tip end portions of the adjacent pins  308 b is large in comparison with the size of the pistons  304  and  305  used in this embodiment (in this case, the cross-sectional area in the direction perpendicular to the drive direction) or the size of the pressurized air gas introduction ports  323  and  324  (more exactly, an outer diameter of a connector used when a tube for introduction of the pressurized air to each port is connected), it is possible to arrange simply these components in parallel with each other. However, in the case where it is necessary to reduce the interval between the pin tip portions in comparison with the size of these pistons or the ports, it is possible to arrange the respective adjacent pistons, i.e., the adjacent recess portions for receiving the pistons in astaggered manner, to arrange the respective adjacent ports in the staggered manner or to combine these components. 
     The example in which these components are combined is shown in  FIGS. 24 and 25 .  FIG. 24  is a view of the base  301  as viewed from the rear side.  FIG. 25  is a view corresponding to  FIG. 23  of the embodiment in which the ports are not arranged in a staggered manner. As is apparent from  FIG. 24 , it is possible to increase the number of the ports considerably in comparison with the case where the ports  323  and  324  are arranged in parallel. Furthermore, as shown in  FIG. 25 , not only is the arrangement of the ports  323  and  324  displaced but also the depths of the adjacent recess portions  321  are different to arrange the cylinder syringes and the pistons not in parallel but in a staggered manner. With such an arrangement, it is possible to reduce the interval between the adjacent pins  308 b not depending upon the size of the pistons and the ports. 
     The arrangement of the ports and the pistons in this modification is simply an example and the arrangement may be displaced more complicatedly so as to make it possible to reduce the distance between the adjacent pins more. Also, in this embodiment, the pressurized gas is used as the drive source. It is however possible to use the liquid such as hydraulic fluid. Also, in this embodiment, the correcting drive means is constituted by a pair of correcting drive members composed of the pistons the cylinder syringes and the like. However, it is possible to compose one of the correcting drive members of piston, cylinder syringe and the like, and the other correcting drive member of elastic material such as spring or rubber. Furthermore, the modifications or the like of each structure described in conjunction with the mode of the first embodiment such as the modification of the structure of the balancing actuators may be applied to this embodiment in the same manner. 
     (Fourth Embodiment) 
     A polishing apparatus for a magnetic head in accordance with a fourth embodiment of this invention will now be described with reference to the accompanying drawings. Incidentally, since the difference between the third embodiment and the fourth embodiment is the structure of the bend correcting mechanism  300  and the bend correcting mechanism  400 , the duplicated description as to the portions except for the correcting mechanisms  400 , the control blocks for detecting the necessary polishing amount of the object  92  to be polished or the like in the overall structure of the apparatus will be omitted. The correcting mechanism  400  in accordance with the fourth embodiment of this invention will now be described in detail. 
       FIG. 26  is a side elevational view of the polishing head according to this embodiment.  FIGS. 27 ,  28  and  29  are a plan view, a frontal view and a cross-sectional view taken along the line  29 — 29  of  FIG. 28 , respectively of the correcting mechanism  400  in accordance with this embodiment. The correcting mechanism  400  in accordance with this embodiment is composed of a base  401 , cylinder syringes  402 ,  403 , pistons  404 ,  405 , a guide bracket  406 , a positioning (fixing) pin  407 , positioning pins  407 a and levers  408 . 
     The base  401  is fixed substantially in parallel to the back plate  68  to only the upper portion by means of screws to thereby fix the correcting mechanism  400  per se the back plate  68 . A recess portion  421  that is composed of a top surface  421 a, a bottom surface  421 b and a vertical surface  421 c is formed on the surface opposite (hereinafter referred to as top surface) to the back plate  68  in the lower portion of the base  401 . Also, pressurized gas introduction ports  423 ,  424  that are pressure medium introduction ports are provided on the surface on the back plate side (hereinafter referred as to as rear side surface). The pressurized gas introduced through the ports is introduced into the top surface  421 a and the bottom surface  421 b through gas passages  425  and  426  that are medium flow paths formed in the interior of the base  401 . 
     A guide groove is provided in the drive direction (hereinafter referred to as vertical direction) of the balancing actuators  70 A and  70 B in the guide bracket  406 . The surface side where the guide groove is formed is faced to the top surface side of the base  401  so that the lever  408  is held slidable in the vertical direction in the guide groove. The lever  408  is composed of a linear shaped portion which pivotally supports at one end about a shaft  420  which is supported by the base  401  and provided at the other end with the pin  408 b, and a driven portion fixed at one end to this linear shaped portion and provided at the other end with a convex portion  408 a received in the recess portion  421  and received in the guide groove except for the convex portion  408 a. The recess portions  421  further receives the pistons  404  and  405  in contact with the convex portion  408 a up and down in the vertical direction of the convex portion  408 a, and the cylinder syringes  402  and  403  for receiving the pistons  404  and  405  slidably in the vertical direction, respectively. 
     For instance, in the case where the pressurized gas is introduced into the pressurized air introduction port  423 , the pressurized air that reaches the top surface  421 a through the gas flow path  425  drives the piston  404  within the cylinder syringe  402  upwardly in the vertical direction. The piston  405  is also in contact with the convex portion  408 a of the lever  408 . However, in this case, since the force of the piston  404  for driving downwardly the convex portion  408 a is stronger, the convex portion  408 a is driven substantially downwardly. The convex portion  408  is driven downwardly, to rotationally drive the lever  408  about the shaft  420 , so that the pin  408 b is moved substantially in the vertical direction. Also, in the case where the lever  408  and the pin  408 b are to be driven substantially upwardly, it is sufficient to introduce the pressurized gas into the pressurized gas introduction port  424 . It is possible to adjust the drive amount of the lever  408  and the pin  408 b by the adjustment of the pressure balance of the gas to be introduced to the port  423  and the port  424 . 
     Incidentally, since the fixture of the jig  94  to the base  401 , the fixture of the probe units  109  and  110 , the deformation of the jig  94  and the object  92  to be polished due to the insertion of the tip end portion of the pin  408 b into the load receiving hole  146  of the jig  94  and the like are the same as those of the third embodiment, the detailed explanation thereof will be omitted. 
     Incidentally, since the interval between the tip end portions of the adjacent pins  408 b is large in comparison with the size of the pistons  404  and  405  used in this embodiment (in this case, the cross-sectional area in the direction perpendicular to the drive direction) or the size of the pressurized air gas introduction ports  423  and  424 , it is possible to simply arrange these components in parallel with each other. However, in the case where it is necessary to reduce the interval between the pin tip portions in comparison with the size of these pistons or the ports, it is possible to arrange the respective adjacent pistons, i.e., the adjacent recess portions for receiving the pistons in a staggered manner, to arrange the respective adjacent ports in the staggered manner or to combine these components. 
     The example in which these components are combined is shown in  FIGS. 30 and 31 .  FIG. 30  is a view of the base  401  as viewed from the rear side.  FIG. 31  is a view corresponding to the embodiment of  FIG. 29  in which the ports are not arranged in a staggered manner. As is apparent from  FIG. 30 , it is possible to increase the number of the ports considerably in comparison with the case where the ports are arranged in parallel. Furthermore, as shown in  FIG. 31 , not only is the arrangement of the ports displaced but also the depths of the adjacent recess portions  421  are different to arrange the cylinder syringes and the pistons not in parallel but in a staggered manner. With such an arrangement, it is possible to reduce the interval between the adjacent pins  408 b not depending upon the size of the pistons and the ports. 
     The arrangement of the ports and pistons in this modification is simply an example and the arrangement may be displaced more complicatedly so as to make it possible to reduce the distance between the adjacent pins more. Also, in this embodiment, the pressurized gas is used as the drive source. It is however possible to use the liquid such as hydraulic fluid. Furthermore, the modifications or the like of each structure described in conjunction with the mode of the first embodiment, such as the modification of the structure of the balancing actuators, may be applied to this embodiment in the same manner. 
     According to the machining apparatus and machining method according to this invention, it is possible to impart the complicated deformation or the like to the object to be machined such as a ceramic bar, and to thus suppress the non-uniformity of the machining amount of the object to be machined upon the machining work of the object to be machined.