JP4024789B2 - Lapping machine and lapping method - Google Patents

Description

  The present invention generally relates to a lapping machine and a row tool for lapping a workpiece, and more particularly to a lapping machine and a row tool suitable for mass production of a homogeneous magnetic head.

  For example, in a magnetic head manufacturing process, after a magnetic head thin film is formed on a substrate, the magnetic head thin film is lapped. By this lapping process, the magnetoresistive layer and gap height of the magnetic head thin film are made constant. Submicron precision is required for the magnetoresistive layer and gap height. For this reason, wrapping machines are also required to process workpieces with high accuracy.

  1A and 1B are explanatory views of a composite magnetic head. As shown in FIG. 1A, the composite magnetic head has a magnetoresistive element 2 formed on a substrate 1 and a write element 5.

  The magnetoresistive element 2 includes a magnetoresistive film 3 and a pair of conductor films 4 connected to both ends of the magnetoresistive film 3 as shown in FIG. The magnetoresistive element 2 is an element whose resistance value is changed by an external magnetic field. Therefore, by using the magnetoresistive element 2, for example, a current having a magnitude corresponding to the magnetization of the track T of the magnetic disk can be output, and data recorded on the magnetic disk can be read.

  Since the magnetoresistive element 2 can only perform reading, a writing element is provided separately when writing is necessary. Here, the writing element 5 comprises an inductive head.

  The writing element 5 includes a lower magnetic pole 6 and an upper magnetic pole 8 that faces the lower magnetic pole 6 with a gap. A coil 7 for exciting the magnetic poles 6 and 8 is provided between the magnetic poles 6 and 8. A nonmagnetic insulating layer 9 is provided around the coil 7.

  In such a composite magnetic head, it is desirable that the resistance value of the magnetoresistive film 3 of the magnetoresistive element 2 is constant in each head. However, it is difficult to make the resistance value constant only by the thin film manufacturing process of the magnetic head. For this reason, after the thin film of the magnetic head is formed, a constant resistance value is obtained by processing so that the height (width) h of the magnetoresistive film 3 becomes constant.

  FIGS. 2A to 2C and FIGS. 3A to 3D are views for explaining a manufacturing process of the composite magnetic head.

  As shown in FIG. 2A, a large number of composite magnetic heads 11 are formed on the wafer 10 by thin film technology. Next, as shown in FIG. 2B, the row bar 11 is produced by cutting the wafer 10 into strips. The row bar 11 is composed of one row of magnetic heads 12. Further, a resistance element 12a for processing monitoring is provided at the left end, the center, and the right end of the row bar 11, for example.

  As described above, the magnetic head 12 is lapped so that the height of the magnetoresistive film 3 is constant. However, the row bar 11 is extremely thin, for example, its thickness is about 0.3 mm. For this reason, it is difficult to attach the row bar 11 directly to the wrapping machine, and the row bar 11 is once bonded to the row tool 13 with hot melt wax as shown in FIG.

  Then, as shown in FIG. 3A, the row bar 11 bonded to the row tool 13 is lapped on the lapping surface plate 14. At this time, as is known in Japanese Patent Laid-Open No. 2-124262 (US Pat. No. 5,239,911) and Japanese Patent Laid-Open No. 5-123960, the resistance value of the processing monitor resistance element 12a of the row bar 11 is always constant during lapping. Measured. Based on the measured resistance value, it is detected whether or not the magnetoresistive film of the magnetic head 12 has reached a target height.

  When it is detected by measuring the resistance value that the magnetoresistive film has been processed to the target height, the lapping is stopped. Thereafter, as shown in FIG. 3B, a large number of sliders are formed on the lower surface 11-1 of the row bar 11.

  Further, as shown in FIG. 3C, the row bar 11 is cut into a plurality of magnetic heads 12 while being bonded to the row tool 13. Then, as shown in FIG. 3D, each magnetic head 12 is taken out while heating the wax tool 13 to melt the hot-melt wax.

In this manner, the row bar 11 composed of one row of magnetic heads 12 is manufactured and lapping is performed for each row bar 11, so that the magnetoresistive films of a large number of magnetic heads 12 can be lapped at a time.
International Publication No. 98/19828 Pamphlet Japanese Patent Laid-Open No. 11-42525

  However, the height of the magnetoresistive film 3 of each magnetic head in the row bar 11 varies depending on the order of submicrons depending on the accuracy of attachment and the accuracy of film formation. Therefore, in order to mass-produce magnetic heads with uniform characteristics, it is necessary to perform lapping while correcting this kind of variation.

  In view of such technical problems, conventionally, a hole penetrating the row tool 13 is provided in the vicinity of the work surface to which the row bar 11 is bonded, and the force from the actuator acts on the row tool 13 through the hole. Thus, a desired pressure distribution is generated between the row bar 11 and the lapping surface of the lapping platen 14. However, if there is a single hole, there is a problem that it is difficult to cope with various variations and it is difficult to obtain a high processing accuracy.

  In order to cope with this, it has been proposed to form a plurality of holes in the row tool 13 as in US Pat. No. 5,607,340, and to apply the force of the actuator to the row tool 13 through each hole.

  However, in order to obtain a desired pressure distribution, the ability to apply a relatively large force to each actuator is required. There is a problem that the interval between the points (holes) cannot be reduced so much that it is difficult to improve the processing accuracy.

  Therefore, an object of the present invention is to provide a wrapping machine and a wrapping method suitable for increasing processing accuracy.

  According to a first aspect of the present invention, there is provided a lapping machine for polishing a row bar for obtaining a plurality of head sliders. A lapping machine acts on a lapping surface plate that provides a lapping surface, a lapping tool that has a work surface that presses the row bar against the lapping surface, and a given pressure distribution between the lapping surface and the lapping tool. Mechanism. The row tool has a plurality of holes arranged along the work surface. The mechanism includes a plurality of links each having a point of action that applies a force in the direction perpendicular to the workpiece surface within the hole to the row tool. Each of the plurality of links has a fulcrum serving as the center of rotation and a force point that receives a force in a direction substantially parallel to the work surface. The ratio of the first distance between the action point and the fulcrum and the second distance between the force point and the fulcrum is substantially constant.

  According to this configuration, for example, even when the action points are arranged in a line and the force points are alternately shifted, the propagation efficiency of the force from the force point to the action point can be kept constant. It is easy to reduce the distance between the points, and a desired pressure distribution can be generated between the row bar and the lapping surface. As a result, the processing accuracy is improved and the object of the present invention is achieved.

  According to a second aspect of the present invention, there is provided a lapping machine for polishing a row bar for obtaining a plurality of head sliders. A lapping machine acts on a lapping surface plate that provides a lapping surface, a lapping tool that has a work surface that presses the row bar against the lapping surface, and a given pressure distribution between the lapping surface and the lapping tool. Mechanism. The row tool is a row tool according to the second aspect of the present invention. The mechanism also includes a plurality of links that apply a force in the direction perpendicular to the work surface within the hole to the row tool.

  According to the present invention, there is an effect that it is possible to provide a lapping machine and a lapping method suitable for increasing processing accuracy.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

  4, 5 and 6 are a plan view, a partially broken side view and a partially broken front view showing an embodiment of a lapping machine according to the present invention.

  As shown well in FIG. 4, the lapping platen 14 that provides the lapping surface 14A is rotated in the direction of arrow A by a motor (not shown). A lap base 24 is supported on the rotary shaft 20 fixed to the wrapping machine via an arm 22, and at the time of wrapping, the lap base 24 is centered on the rotary shaft 20 in the direction of arrow B by a drive mechanism (not shown). Rocks.

  As shown in FIG. 5, the adapter 26 is point-supported by a ball 28 fixed to the lap base 24. A plurality of (for example, four) seat surfaces 30 are provided on the lower surface of the lap base 24, and the seat surfaces 30 slide on the wrapping surface 14A. A row tool 32 is attached to the lower part of the adapter 26.

  As shown in FIG. 7, the row tool 32 includes a pair of holes 321 for attaching the row tool 32 to the adapter 26 and a plurality of (here, seven) holes 322 for elastically deforming the row tool 32 by a mechanism described later. And the work surface 323 to which the row bar 11 is bonded with, for example, hot-melt wax. A plurality of grooves 324 are formed on the work surface 323 for dicing the row bar 11. The holes 322 are arranged along the work surface 323 and are equally spaced here.

  Referring to FIG. 5 again, the row tool 32 is attached to the adapter 26 by inserting a pair of protrusions 34 provided on the adapter 26 into the holes 321 of the row tool 32. Since the adapter 26 is point-supported by the ball 28, the row bar 11 is pressed against the lapping surface 14 </ b> A by the work surface 323 of the row tool 32.

  In this embodiment, four short links 36, three long links 38, and an air cylinder 40 are used in order to generate a given pressure distribution between the row bar 11 and the lapping surface 14A. Each of the links 36 and 38 is connected to a cylinder rod 44 of the air cylinder 40 by a connector 42.

  FIG. 8 is a diagram for explaining the operation of the long link 38 and the short link 36. Each of the short link 36 and the long link 38 has a force point P1 that receives a force in a direction substantially parallel to the work surface 323 by the cylinder rod 44, a fulcrum P2 that is a center of rotation, and a substantially vertical position to the work surface 323 in the hole 322. And an action point P3 for applying a force in a different direction to the row tool 32.

  For example, when the cylinder rod 44 is pushed out and the force point P1 is displaced in the right direction in FIG. 8, the action point P3 is displaced in the same downward direction, and the force for pressing the row bar 11 against the lapping surface 14A increases. On the other hand, when the cylinder rod 44 is pulled and the force point P1 is displaced in the left direction, the action point P3 is displaced in the same upward direction, and the force pressing the row bar 11 against the lapping surface 14A is reduced.

  As shown in FIG. 9, the short links 36 and the long links 38 are alternately arranged. The fulcrum P2 of the short link 36 is provided by a shaft 46 that rotatably supports the short link 36. Further, the fulcrum P2 of the long link 38 is provided by a shaft 48 that rotatably supports the long link 38.

  Since the distance between the fulcrum P2 and the action point P3 in the short link 36 is shorter than the same distance in the long link 38, the shaft 46 is located between the shaft 48 and the action point P3. Each short link 36 has a hole 51 through which the shaft 48 is loosened. Similarly, the long link 38 has a hole (not shown) through which the shaft 46 is loosely penetrated. The shafts 46 and 48 are fixed to the adapter 26.

  10A and 10B are diagrams showing design examples of the long link 38 and the short link 36, respectively. As shown in FIG. 10A, in the long link 38, the distance between the fulcrum P2 and the action point P3 is set to L1, and the distance between the fulcrum P2 and the force point P1 is set to L2.

  As shown in FIG. 10B, in the short link 36, the distance between the fulcrum P2 and the action point P3 is set to L3 (L3 <L1), and the distance between the fulcrum P2 and the force point P1 is L4. Set to

  According to the first aspect of the present invention, L2 / L1 = L4 / L3 is satisfied.

  According to the combination of the short link 36 and the long link 38 as shown in FIG. 9, the straight line along the four force points P1 of the short link 36 and the straight line along the three force points P1 of the long link 38 are different. As shown, it is possible to apply an air cylinder 40 in which cylinder rods 44 are arranged alternately.

  Each cylinder rod 44 is controlled by a pair of air tubes 50 and 52. When the air tube 50 side is set to a positive pressure and the air tube 52 side is set to a negative pressure, the cylinder rod 44 is pulled into the air cylinder 40, and conversely, the air tube 50 side is set to a negative pressure and the air tube 52 is pulled. When the side is set to a positive pressure, the cylinder rod 44 is pushed out from the air cylinder 40.

  According to the first aspect of the present invention, since the above relational expression is satisfied, the force point P1 is required to generate the same force at the action point P3 between the short link 36 and the long link 38. Can be the same force.

  Further, by alternately arranging the cylinder rods 44 as shown in FIG. 11, the distance between the short links 36 and the long links 38 can be reduced while sufficiently increasing the force applied by each cylinder rod 44. Processing accuracy is increased.

  Referring to FIG. 6 again, the table 54 fixed to the lap base 24 is provided with a pressure cylinder 56 and a pair of balance cylinders 58 and 60. The pressure cylinder 56 presses the generally central portion of the adapter 26 in order to apply a uniform pressing force to the row tool 32.

  By using the pressurizing cylinder 56, it is sufficient that the air cylinder 40 has an ability to generate a deviation in a necessary pressure distribution, and the capacity of the air cylinder 40 can be reduced.

  The balance cylinders 58 and 60 press the left end and the right end of the upper surface of the adapter 26 in FIG. 6 in order to correct the balance of the pressing force applied to the row tool 32 in the longitudinal direction of the row tool 32. Also by using the balance cylinders 58 and 60, the capacity of the air cylinder 40 can be reduced as in the case of using the pressure cylinder 56.

  As shown in FIG. 12, the row bar 11 includes a plurality of magnetic heads 12 and a processing monitoring resistance element (ELG element (ELG is an abbreviation for Electrical Lapping Guide)) 12 a. Here, the ELG elements 12a are provided at three locations on the left end, the center, and the right end of the row bar 11.

  As shown in FIG. 13, the ELG element 12a includes an analog resistor 12-1 and a digital resistor 12-2. The analog resistor 12-1 has a pattern in which the resistance value increases as the resistance film decreases. The digital resistor 12-2 has a pattern that turns off when the resistance film decreases to a certain value.

  Accordingly, an equivalent circuit of the ELG element 12a is as shown in FIG. 14A, and the analog resistor 12-1 is indicated by a variable resistor. As shown in FIG. 14B, the resistance value increases as the height of the ELG element 12a decreases.

  An equivalent circuit of the digital resistor 12-2 is represented by five switch resistors as shown in FIG. Then, as shown in FIG. 14B, a broken line-like change is shown at the OFF position of the resistance.

  The resistance value of the ELG element 12a indicates the height of the ELG element 12a. The relationship between the resistance value Ra of the analog resistor 12-1 and the height h of the ELG element 12a is approximated by the following equation.

Ra = a / h + b
The coefficients a and b can be obtained by experiments in advance. However, this characteristic varies depending on the process conditions of each wafer. A digital resistor 12-2 is provided to compensate for this.

  The off positions h1 to h5 of the digital resistor 12-2 are known in advance. When the digital resistor 12-2 is turned off, the measured resistance value and the off position at that time are substituted into the above equation. If the two off points of the digital resistor 12-2 are detected, the coefficients a and b in the above equation can be obtained.

  By this equation, the analog resistance value Ra is converted into the height h of the ELG element 12a. Thus, the height of the ELG element 12a can be obtained by measuring the measured value of the ELG element 12a. Therefore, it can be determined whether or not the height of the ELG element 12a has reached the target value. When the height of the ELG element 12a reaches the target value, the lapping process is stopped.

  In the row bar 11 shown in FIG. 12, three ELG elements 12a are shown. However, in order to control these independently using the seven links 36 and 38 as in this embodiment, more ELG elements 12a are used. It is desirable to use ELG elements 12a (for example, 31 elements).

  At the time of lapping, the pressure distribution is set so as to be generated between the row bar 11 and the lapping surface 14A so that the resistance values of these ELG elements 12a become equal. Such a pressure distribution can be set by feedback-controlling each of the links 36 and 38 based on the resistance measurement value of each ELG element 12a.

  Alternatively, the operation amount of each of the links 36 and 38 may be obtained by calculation based on the resistance value of the ELG element 12a, and the pressure distribution between the row bar 11 and the lapping surface 14A may be set by feedforward control.

  Furthermore, the control of the pressurization amount of the pressurizing cylinder 56 and balance cylinders 58 and 60 can also be performed by feedback control or feedforward control based on the measured resistance value of the ELG element 12a.

  By the way, since the row tool 32 shown in FIG. 7 is generally made of metal, if only the hole 322 is used to deform the work surface 323, a force for unit deforming the work surface 323 is used. Will become bigger.

  Further, when a force is applied to one hole 322, the deformation of the work surface 323 due to the force may spread over a wide range, and independent control by each hole 322 may be difficult. An embodiment of a row tool that improves this point will be described below.

  FIG. 15 is a front view of another row tool 32 'applicable to the present invention. The row tool 32 ′ further includes a plurality of (seven in the drawing) first slits 325 and a plurality of (six in the drawing) second slits 326 in contrast to the row tool 32 shown in FIG. 7. Characterized by dots.

  Each first slit 325 is formed so as to surround each hole 322, and has a substantially C-shape opened toward the work surface 323. Each of the second slits 326 is formed so as to surround the end portions of the two adjacent first slits 325 and has a substantially C-shape that opens toward the opposite side of the work surface 323.

  In this embodiment, in order to make the two holes 322 at both ends have the same properties as the other holes 322, L-shaped third slits 327 are formed in the vicinity of the two holes 322 at both ends. .

  Each slit can be formed by wire electric discharge machining, for example. In FIG. 15, the end portion of each slit or a bulging portion in the middle corresponds to a small hole formed in advance for performing the initial setting of this kind of wire electric discharge machining.

  FIGS. 16A and 16B are diagrams showing models obtained by analyzing the deformation of the row tool 32 ′ shown in FIG. 15 by the finite element method. FIG. 16A shows an analysis model of deformation when a load is applied downward to the second hole 322 from the right, and FIG. 16B shows an upward load applied to the same hole 322. An analysis model of deformation when applied is shown.

  By forming the first and second slits 325 and 326 according to the row tool 32 ′ of the present invention, first, the load to each hole 322 required for unit deformation of the work surface 323 is shown in FIG. It is clear that it is sufficiently smaller than the row tool 32 shown in FIG. 2, and secondly, it is clear that the deformation of the work surface 323 does not reach a wide range when a load is applied to one hole 322. . Therefore, the row tool 32 'is suitable for finely setting the pressure distribution between the row bar 11 and the lapping surface 14A, and can increase the processing accuracy.

  FIG. 17 is a graph showing the relationship between the displacement of the work surface 323 and the position on the work surface 323 when a unit load is applied to each hole 322 of the row tool 32 ′ shown in FIG.

  Specifically, the displacement amount of the work surface 323 when a load of 1 kg is applied to each of the seven holes 322 in the upward and downward directions is shown. Since the slits 325 and 326 are formed, deformation almost symmetrical with respect to the upward direction and the downward direction is possible, and the range of deformation of the work surface 323 when a load is applied to one hole 322 is narrowed. You can see that

  The former feature has an effect of facilitating control based on the measured resistance value of the ELG element 12a, and the latter feature has an effect of enabling independent control of each hole 322.

  FIG. 18 is a graph showing the relationship between the displacement of the work surface 323 and the position on the work surface 323 when a unit load is applied to two adjacent holes 322 of the row tool 32 ′ shown in FIG. 15 in the same direction.

  Specifically, the relationship between the displacement of the work surface 323 and the position on the work surface 323 when a load of 1 kg is applied to the second and third holes 322 from the right in the upward and downward directions is shown. .

  When no slit is formed as in the row tool 32 shown in FIG. 7, if a load is applied to the two holes 322 in the same direction, two vertices are generated in the curve corresponding to the curve shown in FIG. 18. It may end up.

  In this case, control based on the resistance measurement value of the ELG element 12a may be difficult. On the other hand, in the row tool 32 ′ shown in FIG. 15, since the slits 325 and 326 are formed, the vertex of each curve shown in FIG. Absent. This is the same even when there are two or more points, and the pressure distribution between the row bar 11 and the lapping surface 14A can be set finely.

  FIG. 19 is a front view of still another row tool 32 ″ applicable to the present invention. The row tool 32 ″ has 15 more holes 322 and more than the row tool 32 ′ shown in FIG. It is characterized by the fact that 15 first slits 325 and 14 second slits 326 are formed.

  When such a large number of holes 322 are formed, the interval between the holes 322 is as small as several millimeters, for example, so that a lapping machine is provided in combination with a mechanism according to the first aspect of the present invention as shown in FIG. By doing so, processing with extremely high accuracy becomes possible.

  In the above description, an actuator including an air cylinder is illustrated as an actuator acting on the row tool. However, an actuator including another driving part such as a solenoid and a piezoelectric element may be employed.

1A and 1B are explanatory views of a composite magnetic head. 2A, 2B, and 2C are explanatory views (No. 1) of the manufacturing process of the composite magnetic head. (A), (B), (C) and (D) of FIG. 3 are explanatory views (No. 2) of the manufacturing process of the composite magnetic head. FIG. 4 is a plan view of a wrapping machine to which the present invention is applied. FIG. 5 is a partially cutaway side view of the wrapping machine shown in FIG. FIG. 6 is a partially cutaway front view of the wrapping machine shown in FIG. FIG. 7 is a front view of a row tool applicable to the present invention. FIG. 8 is an explanatory diagram of the operation of the long link and the short link shown in FIG. FIG. 9 is a perspective view of the long link and the short link shown in FIG. 10A and 10B are diagrams showing design examples of the long link and the short link shown in FIG. FIG. 11 is a perspective view of the air cylinder shown in FIG. FIG. 12 is an explanatory diagram of a row bar applicable to the present invention. FIG. 13 is a configuration diagram of the ELG element shown in FIG. 14A and 14B are explanatory diagrams of the ELG element shown in FIG. FIG. 15 is a front view of another row tool applicable to the present invention. FIGS. 16A and 16B are diagrams showing an analysis model of deformation of the row tool shown in FIG. FIG. 17 is a graph showing the relationship between the displacement of the workpiece surface and the position on the workpiece surface when a unit load is applied to each hole of the row tool shown in FIG. FIG. 18 is a graph showing the relationship between the displacement of the workpiece surface and the position on the workpiece surface when a unit load is applied to two adjacent holes of the row tool shown in FIG. 15 in the same direction. FIG. 19 is a front view of still another row tool applicable to the present invention.

Explanation of symbols

14 Lap surface plate 14A Lapping surface 24 Lap base 26 Adapter 32, 32 ', 32 "Row tool 36 Short link 38 Long link 40 Air cylinder 44 Cylinder rod 56 Pressure cylinder 58, 60 Balance cylinder

Claims (5)

A lapping machine for polishing a row bar for obtaining a plurality of head sliders,
A lapping surface plate that provides a lapping surface;
A row tool having a work surface that presses the row bar against the lapping surface;
A mechanism that acts on the row tool such that a given pressure distribution occurs between the row bar and the wrapping surface;
The row tool has a plurality of holes arranged along the work surface,
The mechanism includes a plurality of links each having an action point that applies a force in a direction perpendicular to the work surface in the hole to the row tool;
Each of the plurality of links has a fulcrum serving as a center of rotation and a force point that receives a force in a direction substantially parallel to the work surface.
A wrapping machine in which a ratio of a first distance between the action point and the fulcrum and a second distance between the force point and the fulcrum is substantially constant. The wrapping machine according to claim 1,
The plurality of links includes a plurality of first links and a plurality of second links arranged alternately,
The first distance of each first link is longer than the first distance of each second link;
The fulcrum of each first link is provided by a first shaft rotatably supporting the first plurality of links;
The fulcrum of each second link is provided by a second shaft that rotatably supports the second plurality of links, the second shaft being located between the first shaft and the working point. ,
Each of the first links has a hole through which the second shaft passes.
Each of the second links is a wrapping machine having a hole through which the first shaft is loosely passed. The wrapping machine according to claim 1,
The row tool includes a plurality of first slits each having a substantially C-shape that is formed so as to surround the holes and open toward the work surface, and two first slits that are adjacent to each other. A wrapping machine having a plurality of second slits that are formed so as to surround an end portion of the workpiece and are open toward the opposite side to the work surface. A lapping machine for polishing a row bar for obtaining a plurality of head sliders,
A lapping surface plate that provides a lapping surface;
A row tool having a work surface that presses the row bar against the lapping surface;
A mechanism that acts on the row tool such that a given pressure distribution occurs between the row bar and the wrapping surface;
The above row tool is
A plurality of holes arranged along the workpiece surface;
A plurality of first slits each having a substantially C-shape, each of which is formed so as to surround each of the holes and opened toward the work surface;
A plurality of second slits each having a substantially C-shape that is formed so as to surround the ends of the two adjacent first slits and that opens toward the opposite side of the work surface;
The mechanism includes a plurality of links each applying a force in the direction perpendicular to the work surface within the hole to the row tool,
Each of the plurality of links has an action point that contacts the row tool in each of the holes, a fulcrum serving as a rotation center of the link, and a force point that receives a force in a direction substantially parallel to the work surface,
A wrapping machine in which a ratio of a first distance between the action point and the fulcrum and a second distance between the force point and the fulcrum is substantially constant. The wrapping machine according to claim 4,
The plurality of links includes a plurality of first links and a plurality of second links arranged alternately,
The first distance of each first link is longer than the first distance of each second link;
The fulcrum of each first link is provided by a first shaft rotatably supporting the first plurality of links;
The fulcrum of each second link is provided by a second shaft that rotatably supports the second plurality of links, the second shaft being located between the first shaft and the working point. ,
Each of the first links has a hole through which the second shaft passes.
Each of the second links is a wrapping machine having a hole through which the first shaft is loosely passed.

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