Warp correction apparatus for plate-like workpiece and warp correction method

A warp correction apparatus includes an elastic mat, a first sheet supply unit which supplies a first clean sheet on the elastic mat, a workpiece holding mechanism which supplies the plate-like workpiece (a frame unit) on the first clean sheet, a second sheet supply unit which supplies a second clean sheet above the first clean sheet, a pressure roller, a first elevator unit which moves the second clean sheet up and down, a second elevator unit which presses the pressure roller toward the elastic mat, and a roller moving mechanism. The pressure roller is moved along an upper surface of the elastic mat by the roller moving mechanism while the frame unit is sandwiched between the elastic mat and the pressure roller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2014-221112, filed Oct. 30, 2014, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a correction apparatus for correcting warping of a plate-like workpiece such as a frame unit which has been cut out from a flexure chain blank sheet for example, and a warp correction method.

2. Description of the Related Art

A hard disk drive (HDD) is used in an information processing apparatus, such as a personal computer. The hard disk drive comprises a magnetic disk rotatable about a spindle, carriage turnable about a pivot, etc. On an arm of the carriage, a disk drive suspension (which will be hereinafter simply referred to as a suspension) is provided. The suspension comprises elements such as a load beam, and a flexure disposed to overlap the load beam. A magnetic head including a slider is mounted on a gimbal portion formed near a distal end of the flexure. The magnetic head is provided with elements for accessing data, that is, for reading and writing data. The load beam and the flexure, etc., constitute a head gimbal assembly.

Various types of flexures have been put to practical use according to the required specification. As an example of the flexure, a flexure with conductors is known. The flexure with conductors includes a metal base made of a thin stainless steel plate, an insulating layer made of an electrically insulating material, such as polyimide, which is formed on the metal base, and a plurality of conductors formed on the insulating layer.

Conventionally, as a means for enhancing the manufacturing efficiency of the flexure, a flexure chain blank sheet disclosed in, for example, JP 5,273,271 B (Patent Literature 1) and JP 5,365,944 B (Patent Literature 2) is known. In order to manufacture the flexure chain blank sheet, a number of flexure elements having the same shape are formed by etching a single stainless steel plate, for example. Further, a conductive circuit portion is formed on each of the flexure elements.

The flexure chain blank sheet is constituted by arranging a plurality of frame units longitudinally or laterally relative to the sheet. Each of the frame units which constitute the flexure chain blank sheet comprises a frame portion and a number of flexure elements arranged at predetermined pitches within the frame portion. In this specification, of the front side and back side of the frame unit, the side on which the conductive circuit portion is provided is referred to as a first surface, and the side opposite to the conductive circuit portion is referred to as a second surface.

The flexure chain blank sheet is cut off for each of the frame units in the manufacturing process of a flexure. That is, a plurality of frame units are cut out from a single flexure chain blank sheet. A frame unit cut out from the flexure chain blank sheet is an example of a plate-like workpiece. For each of the flexure elements provided in the frame unit, operations such as bending processing and mounting on a load beam are performed.

Stress produced in the process of manufacture may remain in the flexure chain blank sheet. Also, by a difference in the thermal expansion or moisture absorptivity, etc., between the conductive circuit portion and the metal base, there are cases where stress remains in the flexure chain blank sheet. Accordingly, even if the flexure chain blank sheet looks straight and planar at a glance, stress is released when the frame unit is cut out from the flexure chain blank sheet, or the flexure elements are individually cut off from the frame portion of the frame unit, which causes the flexure elements to warp. In particular, the first surface (the side on which the conductive circuit portion is provided) may have slight concave warping. Such warping may be called a “recessed warp”.

For example, when some kind of process is to be performed for the flexure element while the conductive circuit portion of the flexure element is made to face upward, pins may be inserted into positioning holes formed near both ends of the flexure element, respectively. However, when the flexure element has the aforementioned “recessed warp”, the positioning accuracy is degraded, such as pins which are inserted into the positioning holes tending to detach easily. Accordingly, depending on a process of handling the flexure element, it is sometimes more convenient if the first surface (the side on which the conductive circuit portion is provided) warps with the first surface being convex (i.e., to have the so-called upward warp).

BRIEF SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a warp correction apparatus which corrects warping of a plate-like workpiece having a first surface and a second surface such that a desired surface of the first surface and the second surface becomes convex, and a method of correcting warping in such a plate-like workpiece.

An embodiment relates to a warp correction apparatus which corrects warping of a plate-like workpiece including a first surface and a second surface, and the warp correction apparatus comprises: an elastic mat including a flat upper surface; a first sheet supply unit configured to supply a first clean sheet on the upper surface of the elastic mat; a workpiece holding mechanism configured to supply the plate-like workpiece on the first clean sheet; a second sheet supply unit configured to supply a second clean sheet above the first clean sheet; a first elevator unit configured to move the second clean sheet up and down relatively with respect to the first clean sheet; a pressure roller which is movable and disposed above the second clean sheet; a second elevator unit configured to press the pressure roller toward the elastic mat; and a roller moving mechanism configured to move the pressure roller along the upper surface of the elastic mat in a state in which the pressure roller is lowered.

According to the structure of this embodiment, it is possible to correct warping of a plate-like workpiece, such as a frame unit which has been cut out from a flexure chain blank sheet, in such a way that a surface on one specific side of the plate-like workpiece becomes convexly curved.

For example, the elastic mat is formed of a resin foam having elasticity, and the pressure roller is made of an elastic material harder than the elastic mat. An example of the first sheet supply unit includes a first supply bobbin configured to deliver an unused portion of the first clean sheet on the elastic mat, and a first take-up bobbin configured to take up a used portion of the first clean sheet on the elastic mat. An example of the second sheet supply unit includes a second supply bobbin configured to deliver an unused portion of the second clean sheet on the first clean sheet, and a second take-up bobbin configured to take up a used portion of the second clean sheet. An ion generator for preventing static electricity from accumulating on the first clean sheet and the second clean sheet may further be provided.

An example of the plate-like workpiece is formed of a frame unit comprising a frame portion, and a plurality of flexure elements formed within the frame portion. The workpiece holding mechanism places the frame unit on the first clean sheet such that a longitudinal direction in each of the flexure elements agrees with a longitudinal direction in the upper surface of the elastic mat. A first positioning hole formed on a side near one of ends of the frame unit in a longitudinal direction, and a second positioning hole formed on a side near the other end in the longitudinal direction may further be provided.

DETAILED DESCRIPTION OF THE INVENTION

A warp correction apparatus for a plate-like workpiece, and a warp correction method according to one embodiment will be hereinafter described with reference toFIGS. 1 to 18.

A hard disk drive (HDD)10shown inFIG. 1comprises a case11, disks13rotatable about a spindle12, a carriage15turnable about a pivot14, and a positioning motor16for turning the carriage15. The case11is sealed by a lid (not shown).

FIG. 2is a cross-sectional view schematically showing a part of the disk drive10. The carriage15is provided with arms17. At a distal end portion of each arm17, a disk drive suspension (hereinafter simply referred to as a suspension)20is mounted. At a distal end of the suspension20, a slider21which serves as a magnetic head is provided. As each disk13rotates at high speed, an air bearing is formed between the disk13and the slider21.

If the carriage15is turned by the positioning motor16, the suspension20moves radially relative to the disk13, and the slider21thereby moves to a desired track of the disk13. The slider21is provided with a magnetic coil for recording data on the disk13, a magneto resistive (MR) element for reading data recorded on the disk13, etc. The MR element converts a magnetic signal recorded on the disk13into an electrical signal.

FIG. 3shows an example of the suspension20. The suspension20comprises a baseplate30, a load beam31, a hinge portion32, and a flexure40with conductors. The flexure40with conductors may be simply referred to as the flexure40. A boss portion30aof the baseplate30is secured to the arm17(FIGS. 1 and 2) of the carriage15.

The flexure40includes a proximal portion40aoverlapping the load beam31, and a tail portion40bextending toward the back (i.e., in the direction indicated by arrow R inFIG. 3) of the baseplate30from the proximal portion40a. The proximal portion40aof the flexure40is secured to the load beam31by fixing means such as laser welding. A tongue41is formed near a distal end portion40cof the flexure40. The slider21(FIGS. 2 and 3) is mounted on the tongue41. A plurality of tail electrodes42are formed in the tail portion40b.

FIG. 4is a cross-sectional view of a part of the flexure40. The flexure40includes a metal base50obtained by etching a plate of austenitic stainless steel, for example, and a conductive circuit portion51formed along the metal base50. The thickness of the metal base50is less than that of the load beam31. The thickness of the load beam31is, for example, 30 to 62 μm, and the thickness of the metal base50is, for example, 18 μm (12 to 25 μm).

The conductive circuit portion51includes an insulating layer52formed on the metal base50, a plurality of conductors53made of copper which are formed on the insulating layer52, and a cover layer54. Each of the insulating layer52and the cover layer54is formed of an electrically insulating material such as polyimide. Openings55and56may be formed at a part of the metal base50. Double-headed arrow A inFIG. 4indicates the thickness direction of the flexure40, and double-headed arrow B indicates the width direction.

FIG. 5is a plan view showing a part of a flexure chain blank sheet60used in a process of manufacturing the flexure40. The flexure chain blank sheet60includes a plurality of frame units61. Each of the frame units61includes a frame portion62constituted of the metal base50, and a plurality of (several tens of to several hundreds of) flexure elements40′ formed at predetermined pitches within the frame portion62.

Each of the flexure elements40′ includes the metal base50(FIG. 4) and the conductive circuit portion51formed on the metal base50, which are the constituent elements of the flexure40. As in the tail portion40bof the flexure40shown inFIG. 4, the conductive circuit portion51includes the insulating layer52formed on the metal base50, the conductors53made of copper which are formed on the insulating layer52, and the cover layer54covering these conductors53.

The frame portion62of the frame unit61includes a pair of lengthwise frames63and64extending longitudinally relative to the flexure element40′ (as indicated by double-headed arrow X inFIGS. 5 and 6), and a pair of lateral frames65and66extending laterally relative to the flexure element40′ (as indicated by double-headed arrow Y). By the lengthwise frames63and64and the lateral frames65and66, the frame portion62which is continuous all around the frame unit61is formed.

A slit70and a connection portion71are formed between lateral frame65of one frame unit61of the frame units61which are adjacent longitudinally relative to the flexure chain blank sheet60(as indicated by double-headed arrow X inFIG. 5) and lateral frame66of the other frame unit61. By the connection portion71, the frame units61are connected to each other.

A first positioning hole72is formed in lateral frame65, which is one of the lateral frames. In the manufacturing process of the flexure40, in order to keep the flexure chain blank sheet60at a predetermined position, a first positioning pin may be inserted into the positioning hole72. A second positioning hole73is formed in the lateral frame66, which is the other one of the lateral frames. In the manufacturing process of the flexure40, a second positioning pin may be inserted into the positioning hole73. The positioning holes72and73are usually formed near end portions of the flexure element40′ in the longitudinal direction thereof, respectively, in order to increase the positioning accuracy. That is, the first positioning hole72is formed on a side near one end of the frame unit61in the longitudinal direction, and the second positioning hole73is formed on a side near the other end in the longitudinal direction.

FIG. 7is a side view which schematically shows a part of the flexure chain blank sheet60. Double-headed arrow X inFIG. 7indicates the longitudinal direction of the flexure element40′. In this specification, the side on which the conductive circuit portion51of the flexure chain blank sheet60is provided is referred to as a first surface61a, and the side opposite to the conductive circuit portion51is referred to as a second surface61b.

Stress produced in the manufacturing process may remain in the flexure chain blank sheet60. Also, by a difference in the thermal expansion or moisture absorptivity, etc., between the conductive circuit portion51and the metal base50, there are cases where stress remains. However, since the frame units61are connected to each other by the connection portion71, at first glance, the flexure chain blank sheet60appears to have a straight planar shape, as shown inFIG. 7.

If, however, the connection portion71of the flexure chain blank sheet60is cut off, and each of the frame units61is brought into an independent unit, as shown inFIG. 8, because the stress existed in the frame unit61is released by the cutting, the frame unit61warps as shown inFIG. 8. In particular, there may be occurrence of warping (the so-called recessed warp) in which the first surface61a(i.e., the side on which the conductive circuit portion51is provided) is slightly curved inwardly.

In the manufacturing process of the flexure40, when the flexure element40′ is handled while the conductive circuit portion51of the frame unit61is made to face upward, pins may be inserted into the positioning holes72and73in order to position the frame unit61. In that case, when the first surface61ahas a concave shape (recessed warp), a problem arises in terms of the positioning accuracy and positioning simplicity, such as having the problem that the pins inserted into the positioning holes72and73tend to detach easily.

For this reason, depending on the process of handling the flexure element40′, it is sometimes more convenient if the first surface61ahas a convex shape (the so-called upward warp), as shown inFIG. 9. Hence, as described below, in the present embodiment, a correction apparatus80for correcting warping of the frame unit61which has been cut out from the flexure chain blank sheet60, and a correction method are disclosed.

FIGS. 10 to 18show the warp correction apparatus80. The warp correction apparatus80is capable of correcting the warping of the frame unit61, which is an example of a plate-like workpiece.FIG. 10is a perspective view of the warp correction apparatus80. Each ofFIGS. 11 to 18is a side view presented schematically to explain the operation of the correction apparatus80.

The warp correction apparatus80comprises a base81, an elastic mat82disposed on the base81, a first clean sheet83disposed on the elastic mat82, a second clean sheet84disposed on the first clean sheet83, a pressure roller85disposed on the second clean sheet84, etc.

The elastic mat82is formed like a plate. The elastic mat82has a flat upper surface82aextending horizontally, and is secured to the base81such that it is parallel to the base81. An example of the elastic mat82is formed of a foam of a resin (elastomer) having rubber elasticity, such as urethane foam, and has uniform hardness along its entire horizontal length. The thickness of the elastic mat82is, for example, approximately 1 to 5 cm, but the elastic mat82may have a thickness other than that as necessary.

The clean sheets83and84are made of a material which can keep the occurrence of dust and adhesion of dust to a minimum. The material may be, for example, a sheet made of continuous fibers or a resin film. An ion generator (an ionizer)86is disposed lateral to the clean sheets83and84in order to prevent accumulation of static electricity.

The first clean sheet83is supplied horizontally on the elastic mat82by predetermined length L by a first sheet supply unit90. The first sheet supply unit90includes a first supply bobbin91and a first take-up bobbin92. The first supply bobbin91delivers an unused portion of the first clean sheet83on the elastic mat82by a predetermined amount. The first take-up bobbin92takes up the used portion of the first clean sheet83on the elastic mat82by a predetermined amount.

The second clean sheet84is supplied on the first clean sheet83by length L, which is the same length as that of the first clean sheet83, in synchronization with the first clean sheet83by a second sheet supply unit95. The second sheet supply unit95includes a second supply bobbin96and a second take-up bobbin97. The second supply bobbin96delivers an unused portion of the second clean sheet84on the first clean sheet83by a predetermined amount. The second take-up bobbin97takes up the used portion of the second clean sheet84by a predetermined amount.

The second sheet supply unit95is mounted on a first elevator unit98which can be moved up and down. The first elevator unit98is moved up and down between a descent limit and an ascent limit by an elevator mechanism including a servo motor and a ball screw. When the second sheet supply unit95is moved to the descent limit, the second clean sheet84overlaps the first clean sheet83.

As shown inFIG. 10, in a state in which the second sheet supply unit95is moved to the ascent limit, gap G in which a workpiece holding mechanism100can be inserted is formed between the first clean sheet83and the second clean sheet84. An example of the workpiece holding mechanism100is configured to hold the frame unit61by a negative pressure (vacuum). The workpiece holding mechanism100is mounted on a movable arm.

The workpiece holding mechanism100is inserted in gap G formed between the first clean sheet83and the second clean sheet84. The workpiece holding mechanism100can place the frame unit (plate-like workpiece)61on the first clean sheet83one by one. Also, the workpiece holding mechanism100can take out the frame unit61placed on the first clean sheet83from the first clean sheet83.

The pressure roller85is formed of a material (for example, hard rubber) having rubber elasticity that is harder than the elastic mat82. When the hardness of the elastic mat82and that of the pressure roller85are compared, the pressure roller85is harder than the elastic mat82. That is, when the surfaces of the two are pressed by a probe of a tester (that is, when a compressive load is applied), the depression of the elastic mat82is greater than that of the pressure roller85.

The pressure roller85is mounted on a second elevator unit110which can be moved up and down. The second elevator unit110is moved up and down between a descent limit and an ascent limit by a driving mechanism including a servo motor and a ball screw. When the pressure roller85is moved to the descent limit, the warp correction apparatus80is brought into a state in which the frame unit61can be sandwiched between the elastic mat82and the pressure roller85. The pressure force of the pressure roller85against the elastic mat82can be adjusted by a position of the descent limit of the pressure roller85and a degree of flexure of an elastic member (for example, a compression spring) incorporated in the second elevator unit110.

By a roller moving mechanism111including a guide which extends horizontally, the second elevator unit110which moves the pressure roller85up and down is reciprocated longitudinally relative to the elastic mat82. That is, the pressure roller85is moved longitudinally (horizontally) relative to the elastic mat82along the upper surface82aof the elastic mat82between a first position shown inFIG. 14and a second position shown inFIG. 15. The first position mentioned here is the position near one end of the elastic mat82in the longitudinal direction. The second position is the position near the other end of the elastic mat82. The pressure roller85is rotatable about axis115extending horizontally. The axis115of the pressure roller85extends widthways relative to the elastic mat82(i.e., orthogonally to length L).

Next, the operation of the warp correction apparatus80will be described referring toFIGS. 11 to 18.

FIG. 11shows the initial state of the warp correction apparatus80. In this initial state, the first elevator unit98and the second elevator unit110are both at an ascended position. Since the second clean sheet84and the pressure roller85are raised, gap G is formed between the first clean sheet83and the second clean sheet84.

As shown inFIG. 12, as the workpiece holding mechanism100is inserted between the first clean sheet83and the second clean sheet84, at least one frame unit61is supplied on the first clean sheet83. At this time, the frame unit61is placed horizontally on the first clean sheet83in such a position that the conductive circuit portion51(that is, the first surface61a) is made to face upward.

Moreover, the frame unit61is arranged such that the longitudinal direction in the flexure elements40′ (as indicated by double-headed arrow X inFIG. 6) agrees with the longitudinal direction in the first clean sheet83(as indicated by L inFIG. 10) when the frame unit61is placed on the first clean sheet83. That is, the workpiece holding mechanism100places the frame unit61on the first clean sheet83such that the longitudinal direction in the flexure elements40′ agrees with the longitudinal direction in the upper surface82aof the elastic mat82.

Next, as shown inFIG. 13, the first elevator unit98is lowered and the second clean sheet84overlaps with the first clean sheet83and the frame unit61. In this way, the frame unit61is sandwiched between the first clean sheet83and the second clean sheet84.

Next, as shown inFIG. 14, as the second elevator unit110is lowered, the pressure roller85is positioned on the descent limit. In this way, the clean sheets83and84are sandwiched between a lower end of the pressure roller85and the elastic mat82. In this state, since the pressure roller85is positioned ahead the frame unit61, the pressure roller85does not press the frame unit61at this time.

After that, as shown inFIG. 15, the second elevator unit110is moved in a first direction indicated by arrow X1along the upper surface82aof the elastic mat82. The frame unit61is disposed between the clean sheets83and84. Accordingly, in a state where the frame unit61is sandwiched between the elastic mat82and the pressure roller85, the pressure roller85moves horizontally while pressing the frame unit61.

Next, as shown inFIG. 16, as the pressure roller85is moved in a second direction indicated by arrow X2along the upper surface82aof the elastic mat82, the pressure roller85returns to its original position. Also at this time, in a state where the frame unit61is sandwiched between the clean sheets83and84, the pressure roller85moves horizontally while pressing the frame unit61.

The pressure roller85is formed of a material which is harder than the elastic mat82(for example, hard rubber). Further, while the elastic mat82is planar, the pressure roller85is cylindrical. The frame unit61is sandwiched between the elastic mat82and the pressure roller85. In this state, the pressure roller85moves longitudinally relative to the frame unit61. Then, a compressive stress is produced on the first surface61aof the frame unit61which is pressed by the pressure roller85, that is, on a side on which the conductive circuit portion51is provided.

Therefore, when the frame unit61is brought to the free state (the state where no external force is applied), the frame unit61comes to be gradually curved (the so-called upward warp) so that the first surface61abecomes slightly convex, as shown inFIG. 9. AlthoughFIG. 9depicts the frame unit61in an exaggerated manner so that the curvature of the frame unit61can be easily understood, the curvature of the actual frame unit61(height H of the first surface61ashown inFIG. 9) takes on a small value which is greater than or equal to 0 μm and less than or equal to several hundreds of micrometers. In order to ensure that height H of the first surface61aof the frame unit61after warp correction takes on a desired value, the hardness of the elastic mat82and the pressure roller85, the diameter of the pressure roller85, the pressure force of the pressure roller85against the elastic mat82(a load by a spring), and the like are optimized.

As shown inFIG. 17, the first elevator unit98and the second elevator unit110are raised, and the second clean sheet84and the pressure roller85are thereby raised. Consequently, gap G is formed between the first clean sheet83and the second clean sheet84again. As the workpiece holding mechanism100(FIG. 12) is inserted into this gap G, the frame unit61on the first clean sheet83is taken out by the workpiece holding mechanism100.

When a series of warp correction process steps (FIGS. 11 to 17) described above is repeated several times, it is possible that a foreign matter such as dust will adhere to the clean sheets83and84. If the foreign matter such as dust adhered to the clean sheets83and84are transferred to the surface of the frame unit61, the quality of the flexure40may be degraded.

Hence, in the present embodiment, as a dust-proof countermeasure, after the correction process (FIGS. 11 to 17) has been repeated several times, the clean sheets83and84are forwarded by fixed length L (FIG. 10), as shown inFIG. 18. In this way, unused new portions of the clean sheets83and84are disposed on the elastic mat82, and the used portions of the clean sheets83and84are taken up. As a result, the foreign matter such as dust which may be adhered to the clean sheets83and84are caught in rolls of the clean sheets83and84. After that, a series of correction process steps (FIGS. 11 to 17) is repeated again.

As described above, a method of manufacturing the frame unit (the plate-like workpiece)61of the present embodiment includes a manufacturing process of the frame unit61([1] and [2] of the following), and a correction process ([3] to [9] of the following).

[1] The flexure chain blank sheet60comprising a plurality of frame units61is manufactured. Each of the frame units61includes the frame portion62and a number of flexure elements40′.

[2] The frame units61of the flexure chain blank sheet60are cut off.

[3] The first clean sheet83is disposed on the elastic mat82(FIG. 11).

[4] The frame unit61is supplied on the first clean sheet83(FIG. 12).

[5] The second clean sheet84is laid over the first clean sheet83and the frame unit61from above (FIG. 13).

[6] The pressure roller85is lowered toward the elastic mat82from above the second clean sheet84(FIG. 14).

[7] The frame unit61is sandwiched between the elastic mat82and the pressure roller85.

[8] The pressure roller85is moved along the upper surface82aof the elastic mat82while the frame unit61is sandwiched between the elastic mat82and the pressure roller85(FIGS. 15 and 16).

[9] The frame unit61is taken out from the first clean sheet83(FIG. 17).

[10] After a series of the above correction process steps [3] to [9] has been repeated several times, the used portions of the clean sheets83and84are taken up by a predetermined amount, and unused portions of the clean sheets83and84are delivered on the elastic mat82(FIG. 18).

As described above, by performing a series of correction process steps [3] to [9] for the frame unit61which has been cut out from the flexure chain blank sheet, the frame unit61can be corrected such that the first surface61ahas a convexly curved shape. Accordingly, during an operation, etc., of handling the flexure element40′ in which it is desirable that the conductive circuit portion51have a convexly curved shape, it is possible to manage the warping of the flexure element40′ to be in a desirable state. Moreover, it is possible to prevent a foreign matter such as dust from adhering to the frame unit61by the above-described process [10] of intermittently supplying unused fresh portions of the clean sheets83and84at suitable timing. Accordingly, this process is advantageous in maintaining cleanliness of the flexure element40′ for which a high cleaning level is required.

When the pressure roller85is rolled on the elastic mat82via the clean sheets83and84as in the present embodiment, static electricity is likely to accumulate on the clean sheets83and84. When the clean sheets83and84become electrostatically charged, a workpiece (for example, the frame unit61) is attracted to the clean sheets83and84, and the position of the workpiece may be shifted. Displacement of the workpiece may adversely affect the warp correction operation or adsorption of the workpiece by the workpiece holding mechanism100. Therefore, the warp correction apparatus80of the present embodiment can prevent the electrostatic charging of the clean sheets83and84by the ion generator86. Thus, the present invention can eliminate the problem caused by the clean sheets83and84, etc., being electrostatically charged, and enables the correction operation by the warp correction apparatus80to be carried out without trouble.

Note that the plate-like workpiece is not limited to a frame unit of the flexure chain blank sheet, and the present invention may be applied to other types of plate-like workpieces. Depending on the type of plate-like workpiece, warping may be corrected such that the second surface becomes convex. Also, needless to say, in carrying out the present invention, each of the elements which constitute the warp correction apparatus may be modified variously, such as modifying the form, material, and arrangement of the elastic mat, first and second clean sheets, pressure roller, etc. For example, it is possible to structure the first sheet supply unit to be movable up and down, so that the first sheet may be moved up and down relative to the second sheet.