Elastic supporting device for reading head of large-diameter steel belt encoder

Abstract

The invention discloses an elastic supporting device for a reading head of a large-diameter steel belt encoder. The elastic supporting device comprises a steel belt mounting ring, the encoder steel belt is adhered to the outer cylindrical surface of the steel belt mounting ring; the elastic supporting box body is positioned on one side of the steel belt mounting ring; the reading head seat is arranged in the elastic supporting box body, and an encoder reading head is mounted in the reading head seat; the elastic supporting structure is arranged at one end, far away from the encoder steel belt, of the reading head seat; and the adjusting mechanism is connected to the top of the elastic supporting box body and is used for adjusting the relative position of the encoder reading head and the encoder steel belt. According to the steel belt type encoder installed on a large diameter, the spring is used for applying pre-tightening force, the design distance between the reading head and the steel belt is kept in combination with the steel ball, and the measuring precision of the encoder can be guaranteed. When equipment is subjected to extreme impact such as an earthquake, the spring structure can buffer impact force in the radial direction of the rotating shaft, and physical collision between the reading head and the steel belt caused by severe impact can be avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic measuring devices, and particularly to an elastic support device for a reading head of a large-diameter steel strip encoder. Background Art

[0002] For the rotating shaft system of an optoelectronic measuring device, an encoder is generally used to implement the measurement and feedback functions of the rotating position, the speed and acceleration of a driving motor. The encoder mainly consists of a grating code disk of a fixed part, a code track steel ring or a code track steel strip and a reading head of a rotating part. The two maintain a certain designed distance D, generally about 1 mm. When the fixed part and the rotating part rotate relative to each other, the change of the triggered optoelectronic signal generates a reading, so as to realize the non-contact measurement of the angular position, speed and acceleration. Sometimes, the fixed part and the rotating part can also be installed by converting each other. Generally, the grating code disk is used for the rotating shaft system with a small diameter below 100 mm, such as an optoelectronic theodolite and a telescope with a diameter below 1 m. The code track steel ring is used for the rotating shaft system with a medium diameter of 100 mm - 500 mm, such as a medium and small-sized optoelectronic telescope with a diameter of 1 m - 2 m. The code track steel strip is used for the medium-diameter and large-diameter rotating shaft systems above 500 m, such as a medium and large-sized optoelectronic telescope with a diameter above 2 m, a large-sized optoelectronic telescope with a diameter above 5 m and a giant optoelectronic telescope with a diameter above 10 m.

[0003] For a grating code disk type encoder, an integral structure with an internal bearing and a coupling is generally adopted. For a code track steel ring type encoder, the reading head adopts a split design. The steel ring is assembled with a fixed shaft by screws, and the reading head is assembled with a rotating body by screws, both belonging to a rigid support structure. After the equipment is installed and adjusted, no adjustment is generally carried out during the process.

[0004] For a code track steel strip type encoder, the reading head also adopts a split design. The steel strip is adhesively mounted on the outer surface or the inner surface of a fixed shaft part. The reading head is connected with the rotating part of the equipment through a transition piece with an adjustment structure. The two maintain a certain designed distance D and do not change with the increase of the diameter of the shaft part. However, for a large-sized and giant optoelectronic telescope with a diameter above 5 m, the sizes of the fixed shaft part and the rotating body part are huge, reaching several meters or even dozens of meters, and are composed of a variety of different metal materials. Under the condition of environmental temperature change, due to different thermal expansion coefficients, the designed distance D between the reading head and the steel strip will change, thereby affecting the reading accuracy of the encoder, and even causing reading failure, ultimately resulting in abnormal operation, shutdown or accidental runaway of the equipment. Moreover, the encoders of large-sized and giant telescopes are expensive. In the case of extreme impacts such as earthquakes, the large amplitudes generated by large-sized equipment may cause the reading head and the steel strip to collide, damaging the reading head and the steel strip of the encoder.

[0005] Based on the above technical problems, those skilled in the art urgently need to develop an elastic support device for the reading head of a large-diameter steel strip encoder that can ensure the measurement accuracy of the encoder and provide buffer force in extreme cases. Summary of the Invention

[0006] The object of the present invention is to provide an elastic support device for the reading head of a large-diameter steel strip encoder that can ensure the measurement accuracy of the encoder and provide buffer force in extreme cases.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] An elastic support device for the reading head of a large-diameter steel strip encoder of the present invention, the elastic support device includes:

[0009] A steel strip mounting ring; and

[0010] An encoder steel strip bonded to the outer cylindrical surface of the steel strip mounting ring;

[0011] An elastic support box body, which is located on one side of the steel strip mounting ring and forms an accommodation space inside;

[0012] A reading head seat arranged in the elastic support box body, an encoder reading head is installed in the reading head seat, and both the upper and lower ends of the reading head seat form a rolling friction structure with the elastic support box body;

[0013] The upper and lower two frame surfaces of the reading head seat on the side close to the encoder steel strip adopt a cylindrical surface coaxial with the steel strip mounting ring, and are provided with a blind hole array along the radial direction of the rotation axis, and two groups of first steel balls are correspondingly arranged inside the blind holes to contact the non-steel strip area of the steel strip mounting ring;

[0014] The elastic support device further includes:

[0015] An elastic support structure installed at one end of the reading head seat away from the encoder steel strip; and

[0016] An adjustment mechanism connected to the top of the elastic support box body for adjusting the relative position between the encoder reading head and the encoder steel strip.

[0017] Further, the elastic support box body includes a chute bottom plate; and

[0018] A top cover installed at the upper end of the chute bottom plate;

[0019] An end cover plate assembled to the chute bottom plate and the top cover on the side away from the encoder steel strip by screws, and a threaded hole is provided in the middle of the end cover plate for cooperating with the elastic support structure.

[0020] Further, at least three blind holes are respectively provided on the upper surface and the lower surface of the reading head base, and second steel balls are arranged in the blind holes. The upper surface and the lower surface of the reading head base respectively form rolling friction structures with the top cover and the chute bottom plate through the second steel balls.

[0021] Further, a threaded hole is provided at the center of the side of the reading head base away from the encoder steel belt, and the elastic support structure includes a threaded adjustment sleeve. A retaining piece is provided at one end of the threaded adjustment sleeve extending into the elastic support box body, and the part of the threaded adjustment sleeve extending out of the elastic support box body is locked and loosened by a nut; and

[0022] A core shaft with one end assembled in the threaded hole of the reading head base and the other end inserted into the threaded adjustment sleeve. The core shaft can rotate and slide relative to the threaded adjustment sleeve;

[0023] A spring sleeved on the outer wall of the core shaft. The threaded adjustment sleeve jointly restricts the spring through the retaining piece, the core shaft and the reading head base and keeps it in a compressed state.

[0024] Further, long through grooves are respectively provided on the surfaces of the chute bottom plate and the top cover close to the encoder steel belt, and buffer pads are embedded in the long through grooves.

[0025] Further, the adjustment mechanism includes an adjustment plate assembled at the upper end of the elastic support box body; and

[0026] A rotating body connecting piece connected to the upper end of the adjustment plate.

[0027] Furthermore, waist-shaped flange hole arrays along the radial direction of the rotation axis are provided on both sides of the top cover and are assembled with the adjustment plate by screws;

[0028] Waist-shaped flange hole arrays along the tangential direction of the rotation axis are provided on both sides of the adjustment plate and are assembled with the rotating body connecting piece by screws. By respectively adjusting the relative positions between the top cover and the adjustment plate, and between the adjustment plate and the rotating body connecting piece, the relative positions of the encoder reading head and the encoder steel belt are adjusted.

[0029] Furthermore, a V-shaped groove is provided on the upper surface of the chute bottom plate, and two second steel balls are installed in the blind holes at the corresponding positions of the reading head base and the V-shaped groove. Five degrees of freedom of the reading head base are jointly restricted by a plurality of the second steel balls, so that the reading head base can freely move along the radial direction of the rotation axis.

[0030] In the above technical solution, an elastic support device for a large-diameter steel belt encoder reading head provided by the present invention has the following beneficial effects:

[0031] An elastic support device for a large-diameter steel strip encoder reading head of the present invention is aimed at a steel strip encoder installed on a large diameter. By applying a pre-tightening force with a spring and combining steel balls to maintain a designed distance between the reading head and the steel strip, it can solve the problem that when the ambient temperature changes, the physical distance between the assembly structures such as the installation base ring and the upper rotating body of the large-size structure changes due to different thermal expansion coefficients, which in turn affects the measurement accuracy of the encoder, and even leads to reading failure, ultimately resulting in abnormal operation, shutdown or accidental runaway of the equipment. Moreover, in the case of extreme impacts such as earthquakes, the spring structure can buffer the impact force along the radial direction of the rotating shaft. Combined with two buffer pads made of polyurethane material, it can avoid physical collisions between the reading head and the steel strip caused by severe impacts and prevent damage to the reading head and the steel strip of the encoder. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0033] Figure 1 3D assembly schematic diagram of an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0034] Figure 2 Radial assembly sectional view of an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention along the rotating shaft;

[0035] Figure 3 An elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention Figure 2 Enlarged view at position C in;

[0036] Figure 4 Tangential A-A sectional view of an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention along the rotating shaft;

[0037] Figure 5 Axial sectional view of an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention along the rotating shaft direction;

[0038] Figure 6 3D part drawing of the chute bottom plate of an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0039] Figure 7 Front view of the chute bottom plate of an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0040] Figure 8 Top view of the chute bottom plate in an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0041] Figure 9 Left view of the chute bottom plate in an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0042] Figure 10 3D part drawing of the top cover in an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0043] Figure 11 Front view of the top cover in an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0044] Figure 12 Bottom view of the top cover in an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0045] Figure 13 Left view of the top cover in an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0046] Figure 14 3D part drawing of the reading head seat in an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0047] Figure 15 Front view of the reading head seat in an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0048] Figure 16 An elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention Figure 15 Step sectional view F-F of the reading head seat;

[0049] Figure 17 An elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention Figure 15 3D part drawing G-G of the reading head seat;

[0050] Figure 18 Top view of the reading head seat in an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0051] Figure 19 Bottom view of the reading head seat in an elastic support device for a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0052] Figure 20 3D part drawing of the threaded adjusting sleeve in the elastic support device of a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0053] Figure 21 Cross-sectional view of the threaded adjusting sleeve in the elastic support device of a large-diameter steel strip encoder reading head provided by an embodiment of the present invention;

[0054] Figure 22 Left view of the threaded adjusting sleeve in the elastic support device of a large-diameter steel strip encoder reading head provided by an embodiment of the present invention.

[0055] Description of reference numerals:

[0056] 1. Steel strip installation ring; 2. Encoder steel strip; 3. Elastic support box; 4. Reading head seat; 5. First steel ball; 6. Elastic support structure; 7. Adjusting mechanism; 8. Encoder reading head; 9. Second steel ball; 10. Buffer pad;

[0057] 301. Chute bottom plate; 302. Top cover; 303. End cover plate; 3011. V-shaped groove;

[0058] 601. Threaded adjusting sleeve; 602. Nut; 603. Core shaft; 604. Spring; 605. Retaining plate;

[0059] 701. Adjusting plate; 702. Rotating body connecting piece. Detailed implementation manners

[0060] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0061] See Figures 1 to 22 as shown;

[0062] An elastic support device for a large-diameter steel strip encoder reading head of the present invention, the elastic support device includes:

[0063] A steel strip installation ring 1; and

[0064] An encoder steel strip 2 bonded to the outer cylindrical surface of the steel strip installation ring 1;

[0065] An elastic support box 3, which is located on one side of the steel strip installation ring 1 and forms an accommodation space inside;

[0066] A reading head seat 4 provided in the elastic support box 3, an encoder reading head 8 is installed in the reading head seat 4 and fixed by screws, and both the upper and lower ends of the reading head seat 4 form a rolling friction structure with the elastic support box 3;

[0067] On the upper and lower border surfaces of the reading head seat 4 close to one side of the encoder steel strip 2, cylindrical surfaces coaxial with the steel strip mounting ring 1 are adopted, and a blind hole array along the radial direction of the rotation axis is provided. Two groups of first steel balls 5 are correspondingly built in at the blind holes to keep in contact with the non-steel strip area of the steel strip mounting ring 1. By designing the depth of the blind holes in combination with the diameter of the first steel balls 5, the radial distance between the encoder reading head 8 and the encoder steel strip 2 along the rotation axis is kept not less than the designed distance D. At the same time, the first steel balls 5 also help to reduce the frictional resistance of relative movement;

[0068] The elastic support device further includes:

[0069] An elastic support structure 6 installed at one end of the reading head seat 4 away from the encoder steel strip 2; and

[0070] An adjustment mechanism 7 connected to the top of the elastic support box body 3 for adjusting the relative positions of the encoder reading head 8 and the encoder steel strip 2.

[0071] As a further introduction of this embodiment, the elastic support box body 3 includes a chute bottom plate 301; and

[0072] A top cover 302 installed at the upper end of the chute bottom plate 301;

[0073] An end cover plate 303 assembled to the chute bottom plate 301 and the top cover 302 on the side away from the encoder steel strip 2 by screws. A threaded hole is provided in the middle of the end cover plate 303 for mating with the elastic support structure 6.

[0074] As a further introduction of this embodiment, at least three blind holes are respectively provided on the upper surface and the lower surface of the reading head seat 4, and second steel balls 9 are provided in the blind holes. The upper surface and the lower surface of the reading head seat 4 respectively form a rolling friction structure with the top cover 302 and the chute bottom plate 301 through the second steel balls 9.

[0075] As a further introduction of this embodiment, a threaded hole is provided at the center of the side of the reading head seat 4 away from the encoder steel strip 2. The elastic support structure 6 includes a threaded adjustment sleeve 601. A retaining piece 605 is provided at one end of the threaded adjustment sleeve 601 extending into the elastic support box body 3. The part of the threaded adjustment sleeve 601 extending out of the elastic support box body 3 is locked and loosened by a nut 602 to keep the pre-tightening force unchanged after adjustment; and

[0076] A core shaft 603 with one end assembled in the threaded hole of the reading head seat 4 and the other end inserted into the inside of the threaded adjustment sleeve 601. The core shaft 603 can rotate and slide relative to the threaded adjustment sleeve 601;

[0077] A spring 604 sleeved on the outer wall of the mandrel 603. The threaded adjusting sleeve 601, through the retaining piece 605, the mandrel 603 and the reading head seat 4, jointly restricts the spring 604 and keeps it in a compressed state, thereby applying a pre-tightening force along the radial direction of the rotating shaft to the reading head seat 4 and the ball set between it and the steel strip mounting ring 1, ensuring that the radial distance between the encoder reading head 8 and the encoder steel strip 2 along the rotating shaft is not greater than the designed distance D. The large end of the threaded adjusting sleeve 601 is designed with a hexagonal head structure with a retaining edge, which is convenient for using a wrench to adjust its relative position with the end cover plate 303, and further adjust the compression degree of the spring 604, and finally realize the adjustment of the pre-tightening force.

[0078] Specifically, the end cover plate 303 is assembled with the chute bottom plate 301 and the top cover 302 on the side away from the encoder steel strip 2 by screws. A threaded hole is designed in the middle of the end cover plate 303, which cooperates with the external thread at the small end of the threaded adjusting sleeve 601.

[0079] As a further introduction of this embodiment, long through slots are opened on the surfaces of the chute bottom plate 301 and the top cover 302 close to the encoder steel strip 2, and buffer pads 10 are embedded in the long through slots. As Figure 3 shown, the buffer pads 10 protrude from the chute bottom plate 301 and the top cover 302 by a height E, and the protruding parts are flush with the encoder reading head 8. In extreme shock situations such as earthquakes, large-sized parts or assemblies generate large amplitudes. The spring 604 and the buffer pads 10 work together to buffer the radial impact force along the rotating shaft, ensuring that the chute bottom plate 301 and the top cover 302 will not collide rigidly with the encoder steel strip 2 and the steel strip mounting ring 1, affecting the encoder accuracy or even damaging the encoder.

[0080] As a further introduction of this embodiment, the adjusting mechanism 7 includes an adjusting plate 701 assembled on the upper end of the elastic support box body 3; and

[0081] a rotating body connecting piece 702 connected to the upper end of the adjusting plate 701.

[0082] As a further introduction of this embodiment, waist-shaped flange hole arrays along the radial direction of the rotating shaft are provided on both sides of the top cover 302, and are assembled with the adjusting plate 701 by screws;

[0083] Waist-shaped flange hole arrays along the tangential direction of the rotating shaft are provided on both sides of the adjusting plate 701, and are assembled with the rotating body connecting piece 702 by screws. By respectively adjusting the relative positions between the top cover 302 and the adjusting plate 701, and between the adjusting plate 701 and the rotating body connecting piece 702, the relative positions of the encoder reading head 8 and the encoder steel strip 2 are adjusted.

[0084] When the ambient temperature changes, the above elastic support structure 6 can prevent the distance between the encoder reading head 8 and the encoder steel strip 2 from changing radially along the rotation axis due to the different coefficients of thermal expansion of the large-diameter steel strip mounting ring 1 at the lower part of the rotation axis system and the related assemblies, and the upper rotating body connecting piece 702 and the related assemblies, so that the designed distance D is always maintained.

[0085] As a further introduction to this embodiment, a V-shaped groove 3011 is provided on the upper surface of the chute bottom plate 301. Two second steel balls 9 are installed in the blind holes at the corresponding positions of the reading head seat 4 and the V-shaped groove 3011. The five degrees of freedom of the reading head seat 4 are jointly restricted by the plurality of second steel balls 9, leaving only one degree of freedom along the radial direction of the rotation axis to realize the free movement of the reading head seat 4 in this direction. Grooves are opened at the corresponding positions on the side surface of the reading head seat 4 and the side surface of the top cover 302 to facilitate the extension of the reading head cable.

[0086] Only some exemplary embodiments of the present invention have been described by way of illustration above. Without doubt, for those of ordinary skill in the art, the described embodiments can be modified in various different ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. An elastic support device for a large diameter steel belt encoder reading head, characterized in that: The elastic supporting device comprises: Steel band mounting ring (1); and An encoder steel belt (2) bonded to the outer cylindrical surface of the steel belt mounting ring (1); An elastic support box (3) is located on one side of the steel belt mounting ring (1) and has a receiving space formed therein; A reading head seat (4) is arranged in the elastic support box (3), an encoder reading head (8) is installed in the reading head seat (4), and the upper and lower ends of the reading head seat (4) form a rolling friction structure with the elastic support box (3); The upper and lower frame surfaces of the reading head seat (4) on the side close to the encoder steel belt (2) are cylindrical surfaces coaxial with the steel belt mounting ring (1), and are provided with a blind hole array along the radial direction of the rotating axis, and two groups of first steel balls (5) are built into the blind holes corresponding to the blind holes to contact the non-steel belt area of ​​the steel belt mounting ring (1); The elastic support device also includes: an elastic support structure (6) mounted on an end of the reading head base (4) away from the encoder steel belt (2); and An adjustment mechanism (7) connected to the top of the elastic support box (3) is used to adjust the relative position of the encoder reading head (8) and the encoder steel belt (2).

2. The elastic support device for a large diameter steel belt encoder reading head according to claim 1, characterized in that: The elastic support box (3) comprises a slide groove bottom plate (301); and A top cover (302) mounted on the upper end of the chute bottom plate (301); An end cover plate (303) is assembled on the side of the slide groove bottom plate (301) and the top cover (302) away from the encoder steel belt (2) by screws, and a threaded hole is provided in the middle of the end cover plate (303) for matching with the elastic support structure (6).

3. The elastic support device for a large diameter steel belt encoder reading head according to claim 2, characterized in that: The upper surface and the lower surface of the reading head seat (4) are respectively provided with at least three blind holes, and second steel balls (9) are provided in the blind holes. The upper surface and the lower surface of the reading head seat (4) form a rolling friction structure with the top cover (302) and the slide groove bottom plate (301) respectively through the second steel balls (9).

4. The elastic support device for a large diameter steel belt encoder reading head according to claim 1, characterized in that: A threaded hole is provided at the center of one side of the reading head seat (4) away from the encoder steel belt (2), and the elastic support structure (6) comprises a threaded adjustment sleeve (601), one end of the threaded adjustment sleeve (601) extending into the elastic support box (3) is provided with a blocking piece (605), and the portion of the threaded adjustment sleeve (601) extending out of the elastic support box (3) is locked and prevented from loosening by a nut (602); and One end is assembled in the threaded hole of the reading head seat (4), and the other end is inserted into the core shaft (603) inside the threaded adjustment sleeve (601), and the core shaft (603) can rotate and slide relative to the threaded adjustment sleeve (601); The spring (604) is sleeved on the outer wall of the core shaft (603), and the threaded adjustment sleeve (601) jointly constrains the spring (604) through the baffle (605), the core shaft (603) and the reading head seat (4), and puts the spring (604) in a compressed state.

5. The elastic support device for a large diameter steel belt encoder reading head according to claim 2, characterized in that: The surfaces of the slide groove bottom plate (301) and the top cover (302) close to the encoder steel belt (2) are both provided with long through grooves, and a buffer pad (10) is embedded in the long through grooves.

6. The elastic support device for a large diameter steel belt encoder reading head according to claim 2, characterized in that: The adjustment mechanism (7) comprises an adjustment plate (701) mounted on the upper end of the elastic support box (3); and A rotating body connecting member (702) is connected to the upper end of the adjusting plate (701).

7. The elastic support device for a large diameter steel belt encoder reading head according to claim 6, characterized in that: The top cover (302) is provided with an array of waist-shaped flange holes along the radial direction of the rotary axis on both sides, and is assembled with the adjustment plate (701) by means of screws; The adjustment plate (701) is provided with an array of waist-shaped flange holes tangential to the rotation axis on both sides, and is assembled with the rotating body connecting member (702) by means of screws. The relative positions of the top cover (302) and the adjustment plate (701), and the adjustment plate (701) and the rotating body connecting member (702) are adjusted respectively, so as to adjust the relative positions of the encoder reading head (8) and the encoder steel belt (2).

8. The elastic support device for a large diameter steel belt encoder reading head according to claim 3, characterized in that: A V-shaped groove (3011) is provided on the upper surface of the slide groove bottom plate (301), and two second steel balls (9) are installed in the blind holes at the positions corresponding to the V-shaped groove (3011) of the reading head seat (4), and the five degrees of freedom of the reading head seat (4) are jointly constrained by the plurality of the second steel balls (9), so that the reading head seat (4) can freely move along the radial direction of the rotary axis.

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