Normally closed braking device and rotary table using the same

Abstract

The normally closed braking device of the present invention includes a housing, in which a rotating disc, a braking ring and a pressurizing ring are provided. When fluid is introduced only into the first chamber, the fluid pushes the braking ring to release the braking state of the rotating disc. When fluid is introduced only into the second chamber, on the one hand, the fluid pushes the braking ring to keep the rotating disc in the braking state, and on the other hand, the fluid pushes the pressurizing ring to compress the elastic unit. The energy generated by the compression of the elastic unit acts on the braking ring through the fluid, so that the braking ring achieves a double pressurizing effect. When the action of the fluid fails, the braking ring can still provide a braking effect on the rotating disc through the elastic unit to improve the operation safety. In addition, the present invention also provides a rotating workbench using the aforementioned normally closed braking device.

Description

Technical Field

[0001] The invention relates to a braking device, in particular to a normally closed braking device and a rotary workbench using the normally closed braking device. Background Art

[0002] In order to prevent the spindle from rotating after processing, a set of brakes is usually configured in the structure to apply braking force to the stationary spindle to keep the spindle stable in a stationary state. However, traditional brakes cannot provide braking force to the spindle under special conditions (such as power outages without warning or pipeline ruptures), which can easily cause damage to the machine and may even endanger the safety of surrounding personnel.

[0003] The normally closed hydraulic brake device disclosed in CN210024594U uses the elastic force of multiple springs to push the piston down when the machine is stopped or in standby mode, so that the brake device is in a clamped state and locks the spindle, thereby preventing the spindle from rotating. When releasing the brake, the hydraulic oil is used to push the piston in the opposite direction, so that the brake device becomes a loose state, and the spindle can operate normally at this time. However, in the aforementioned patent document, the braking force provided by multiple springs alone is very limited, and it is difficult to be applied to heavy cutting and high feed occasions.

[0004] In addition, Figure 1 and Figure 2 The conventional normally closed brake shown therein mainly comprises a brake disc 1, a brake piston 2, a plurality of compression springs 3 and a brake release piston 4, wherein the compression spring 3 constantly applies an axial thrust to the brake disc 1, so that the brake disc 1 maintains a normally closed braking state. When only the brake piston 2 is acted upon by the fluid, an axial thrust is applied to the brake disc 1, such as Figure 1 As shown, the brake disc 1 provides a braking effect on the rotating shaft 5 under the combined action of the brake piston 2 and the compression springs 3; when only the brake release piston 4 is acted upon by the fluid, a reverse thrust is applied to the brake disc 1, overcoming the axial thrust applied by the compression springs 3 to the brake disc 1, as shown in FIG. Figure 2 As shown, the brake disc 1 releases the braking effect on the rotating shaft 5. However, in the above-mentioned prior art, since the fluid force on the brake piston 2 and the elastic force applied to the brake disc 1 by the compression spring 3 have the same force direction, the greater the fluid force on the brake piston 2, the smaller the elastic force generated by the compression spring 3, which will affect the braking effect provided by the brake disc 1 on the rotating shaft 5, and it is difficult to apply it to heavy cutting and high feed occasions. Summary of the invention

[0005] The main purpose of the present invention is to provide a normally closed brake device, which can achieve the effects of double pressurization and normally closed braking to improve operational safety and is suitable for heavy cutting and high feed occasions.

[0006] To achieve the above main object, the normally-closed braking device of the present invention includes a housing, a disc group, a braking ring, a pressure ring, and an elastic unit. The housing has a receiving groove; the disc group is disposed in the receiving groove of the housing and has a first fixed disc, a second fixed disc, and a rotating disc, and the rotating disc is disposed between the first fixed disc and the second fixed disc; the braking ring is movably disposed in the receiving groove of the housing and forms a first chamber with the housing. In addition, the braking ring has a braking portion. When the braking ring is in the braking position, the braking portion of the braking ring presses against the first fixed disc, so that the rotating disc is fixed between the first fixed disc and the second fixed disc. When the braking ring is in the release braking position, the braking portion of the braking ring releases the first fixed disc, so that the rotating disc can rotate relative to the first fixed disc and the second fixed disc; the pressure ring is disposed in the receiving groove of the housing and partially abuts against the braking ring, so that a second chamber is formed between the pressure ring and the braking ring; the elastic unit is disposed on the pressure ring and is used to provide an elastic force to push the pressure ring towards the braking ring.

[0007] As can be seen from the above, when only a fluid is introduced into the first chamber, the braking ring is kept in the release braking position by the action of the fluid. When only the fluid is introduced into the second chamber, the braking ring is kept in the braking position by the action of the fluid, and the pressure ring compresses the elastic unit by the action of the fluid. The direction of the force exerted by the fluid on the pressure ring is opposite to the direction of the force exerted by the elastic unit on the pressure ring. According to Pascal's principle, since the second chamber is in a closed state, the energy generated by the compression of the elastic unit will act on the braking ring through the fluid, so that the braking ring achieves a double pressurization effect. In addition, when no fluid is introduced into the first chamber and the second chamber, the pressure ring is pushed against the braking ring by the force exerted by the elastic unit, so that the braking ring is kept in the braking position to achieve the normally-closed braking effect. In other words, the normally-closed brake of the present invention uses the design of the first chamber and the second chamber in combination with the braking ring and the pressure ring. As long as the fluid is introduced into the first chamber and the second chamber respectively, the braking ring can be controlled to provide a release braking effect and a braking effect on the rotating disc. In addition, in the case where no fluid is introduced into the first chamber and the second chamber or they fail, through the partial braking force provided by the elastic unit, the braking ring can still be kept in the braking position to achieve the normally-closed braking effect, thereby improving the safety in operation.

[0008] Preferably, the brake ring has an inner ring surface, in which a sealing ring and a back-up ring adjacent to the sealing ring are embedded. One side of the pressure ring facing the brake ring has a first flange and a second flange adjacent to the first flange. The first flange of the pressure ring abuts against the brake ring, and the second flange of the pressure ring abuts against the sealing ring and the back-up ring. The sealing ring enhances the sealing effect between the brake ring and the pressure ring. Additionally, the back-up ring enables the brake ring to maintain good balance during operation, preventing the brake ring from skewing and affecting the braking effect.

[0009] Preferably, the braking portion of the brake ring has a braking surface. When the brake ring is in the braking position, the brake ring presses against the first fixed disc with the braking surface of the braking portion. The radial length of the braking surface does not exceed the overlapping area of the first fixed disc, the second fixed disc, and the rotating disc, so as to prevent the brake ring from pressing on the rotating disc or a separating ring disposed between the first fixed disc and the second fixed disc.

[0010] Preferably, the brake ring further has an inner ring surface adjacent to the braking surface, and there is a first included angle between the braking surface and the inner ring surface. The first included angle is less than 90 degrees, so that the first fixed disc can return to its original state in the released braking state and extend its service life.

[0011] Preferably, the first fixed disc has a compressed section. When the brake ring is in the braking position, there is a second included angle between the compressed section of the first fixed disc and the inner ring surface of the brake ring. The second included angle is less than or equal to the first included angle, thus achieving the best clamping effect.

[0012] Preferably, the elastic unit has an elastic body seat and a plurality of elastic bodies. The elastic body seats are disposed in the accommodation groove of the housing and adjacent to the pressure ring, and the elastic bodies are disposed between the pressure ring and the elastic body seats to push the pressure ring towards the brake ring.

[0013] In addition, the present invention further provides a rotary table using the aforementioned normally-closed braking device, which further includes a rotating shaft. The rotating shaft is rotatably disposed in the accommodation groove of the housing and its outer peripheral surface is fixedly connected to the rotating disc. Therefore, when the brake ring is in the braking position, the rotating disc is clamped and fixed between the first fixed disc and the second fixed disc, causing a braking effect on the rotating shaft. When the brake ring is in the released braking position, the rotating disc can move synchronously with the rotating shaft.

[0014] Details of the normally closed braking device provided by the present invention and the rotary table using the normally closed braking device, including its structure, characteristics, assembly, or usage method, will be described in detail in the subsequent embodiments. However, those of ordinary skill in the art of the present invention should understand that these detailed descriptions and the specific embodiments listed for implementing the present invention are only for explaining the present invention and are not intended to limit the scope of the patent application of the present invention. Description of the Drawings

[0015] Figure 1 It is a partial cross-sectional view of an existing normally closed brake, mainly showing the braking effect provided by the brake disc on the rotating shaft.

[0016] Figure 2 It is another partial cross-sectional view of an existing normally closed brake, mainly showing the release of the braking effect of the brake disc on the rotating shaft.

[0017] Figure 3 It is a perspective view of the rotary table of the present invention used in combination with a swinging spindle head.

[0018] Figure 4 It is a perspective view of the rotary table of the present invention.

[0019] Figure 5 It is an exploded perspective view of the normally closed braking device provided by the rotary table of the present invention, with the housing not drawn.

[0020] Figure 6 It is an end view of the rotary table of the present invention.

[0021] Figure 7 For Figure 6 It is a partial cross-sectional view along the cutting line 7-7, mainly showing that the second fluid is not introduced into the second chamber.

[0022] Figure 8 For Figure 6 It is a partial cross-sectional view along the cutting line 8-8, mainly showing that the second fluid is not introduced into the second chamber.

[0023] Figure 9 Similar to Figure 7 It mainly shows that the second fluid is introduced into the second chamber.

[0024] Figure 10 Similar to Figure 8 It mainly shows that the first fluid is introduced into the first chamber.

[0025] Figure 11 It is a partial cross-sectional view of the normally closed braking device of the present invention, mainly showing the structural relationship between the brake ring and the disc group.

[0026] Figure 12Another partial cross-sectional view of the normally closed braking device of the present invention, mainly showing the angular relationship between the brake ring and the disc pack.

[0027] In the above-mentioned drawings, the meanings of the reference numerals are specifically as follows:

[0028] 1: Brake disc

[0029] 2: Brake piston

[0030] 3: Compression spring

[0031] 4: Release brake piston

[0032] 10: Rotary table

[0033] 12: Rotating shaft

[0034] 122: Outer flange

[0035] 14: Swing type spindle head

[0036] 16: First joint

[0037] 18: Second joint

[0038] 20: Normally closed braking device

[0039] 22: First fluid

[0040] 24: Second fluid

[0041] 30: Housing

[0042] 31: Receiving groove

[0043] 32: Inner flange

[0044] 33: First flow channel

[0045] 34: Second flow channel

[0046] 40: Disc pack

[0047] 41: First fixed disc

[0048] 412: Compressed section

[0049] 42: Second fixed disc

[0050] 43: Spacer ring

[0051] 44: Rotating disc

[0052] 45: Screw

[0053] 46: Screw

[0054] 50: Brake ring

[0055] 51: Inner ring surface

[0056] 52: Braking part

[0057] 53: Braking surface

[0058] 54: First chamber

[0059] 55: Sealing ring

[0060] 56: Backing ring

[0061] L: Radial length of the braking surface

[0062] P1: Braking position

[0063] P2: Release braking position

[0064] 60: Pressurizing ring

[0065] 61: First flange

[0066] 62: Second flange

[0067] 63: Second chamber

[0068] 64: Concave hole

[0069] 70: Elastic unit

[0070] 71: Elastic body seat

[0071] 72: Countersunk screw hole

[0072] 73: Elastic body

[0073] 74: Pin

[0074] θ1: First included angle

[0075] θ2: Second included angle Detailed implementation manners

[0076] The applicant hereby explains that throughout the specification, including the embodiments described below and the claims of the patent application, the directional terms are based on the directions in the drawings. Secondly, in the embodiments and drawings to be described below, the same reference numerals represent the same or similar elements or their structural features.

[0077] Please refer to Figure 3 and Figure 4 , the normally closed braking device 20 of the present invention is used in cooperation with a rotating shaft 12 to form a rotary table 10 with the rotating shaft 12. The aforementioned rotating shaft 12 can be assembled with a swinging spindle head 14, so that the swinging spindle head 14 can be driven by the aforementioned rotating shaft 12 to perform a swinging motion. Please refer to again Figures 4 to 5, the normally-closed braking device 20 of the present invention includes a housing 30, a disc group 40, a braking ring 50, a pressure ring 60, and an elastic unit 70.

[0078] The housing 30 has a receiving groove 31 and an inner flange 32. The cross-sectional shape of the receiving groove 31 is circular, and the inner flange 32 protrudes radially from the groove wall of the receiving groove 31. As Figure 4 and Figure 7 shown, the aforementioned rotating shaft 12 is rotatably installed in the receiving groove 31 and is surrounded by the inner flange 32. In addition, the housing 30 further has a first flow channel 33 (as Figure 8 shown) that is radially connected to the receiving groove 31 and a second flow channel 34 (as Figure 7 shown) that is radially connected to the receiving groove 31. The inlet end of the first flow channel 33 is installed with a first joint 16 for injecting a first fluid 22 (here it is hydraulic oil, actually gas can also be used, not limited to hydraulic oil), and the inlet end of the second flow channel 34 is installed with a second joint 18 for injecting a second fluid 24 (here it is hydraulic oil, actually gas can also be used, not limited to hydraulic oil).

[0079] The disc group 40 is disposed in the receiving groove 31 of the housing 30 and has a first fixed disc 41, a second fixed disc 42, a spacer ring 43, and two mutually stacked rotating discs 44. As Figure 5 and Figure 7 shown, the first fixed disc 41, the second fixed disc 42, and the spacer ring 43 are fixed to the inner flange 32 of the housing 30 together by multiple screws 45. Among them, the second fixed disc 42 is closer to the inner flange 32 of the housing 30 than the first fixed disc 41. As for the spacer ring 43, it is located between the first fixed disc 41 and the second fixed disc 42 and separates the two. Again, as Figure 7 shown, the outer peripheral edges of the two rotating discs 44 are located between the first fixed disc 41 and the second fixed disc 42, and the inner peripheral edges of the two rotating discs 44 are fixed to an outer flange 122 of the rotating shaft 12 by multiple screws 46, so that the two rotating discs 44 can rotate together with the rotating shaft 12.

[0080] The braking ring 50 is disposed in the receiving groove 31 of the housing 30 in a manner that can move back and forth and forms a first chamber 54 communicating with the first flow channel 33 with the housing 30 (as Figure 8 shown). The front and rear ends of the first chamber 54 are respectively closed by the housing 30 and the braking ring 50. The braking ring 50 is adjacent to the disc group 40, and a braking portion 52 protrudes from one side surface of the braking ring 50 toward the disc group 40. When the braking ring 50 is located as Figure 9In the braking position P1 shown in FIG. 1 , the braking ring 50 presses the first fixed disc 41 with the braking portion 52, so that the first fixed disc 41 is elastically deformed and the rotating disc 44 is clamped and fixed between the first fixed disc 41 and the second fixed disc 42. Figure 10 In the brake release position P2 shown, the brake portion 52 of the brake ring 50 releases the first fixed disc 41 to restore the first fixed disc 41 to its original state. At this time, the rotating disc 44 can rotate relative to the first fixed disc 41 and the second fixed disc 42 along with the rotating shaft 12 .

[0081] The pressure ring 60 is disposed in the groove 31 of the housing 30 and adjacent to the brake ring 50. The pressure ring 60 extends a first flange 61 and a second flange 62 adjacent to the first flange 61 toward one side of the brake ring 50. Figure 7 As shown, the pressure ring 60 abuts against the brake ring 50 with the first flange 61, so that a second chamber 63 is formed between the pressure ring 60 and the brake ring 50. The outer side of the second chamber 63 is connected to the second flow channel 34, and the inner side of the second chamber 63 is closed by the first flange 61. Figure 7 As shown, the pressure ring 60 abuts against the inner ring surface 51 of the brake ring 50 with the second flange 62. A sealing ring 55 and a back-drag ring 56 adjacent to the sealing ring 55 are embedded in the inner ring surface 51 of the brake ring 50. On the one hand, the sealing ring 55 increases the sealing effect between the two. On the other hand, the back-drag ring 56 enables the brake ring 50 to maintain a good balance during operation to avoid the brake ring 50 from being skewed and affecting the braking effect.

[0082] The elastic unit 70 is disposed in the receiving groove 31 of the housing 30 and has an annular elastic body seat 71, a plurality of elastic bodies 73 (compression springs are used as an example here) and a plurality of pins 74. The elastic body seat 71 is fixedly disposed in the housing 30 and adjacent to the pressure ring 60. The pressure ring 60 has a plurality of concave holes 64 (such as Figure 7 As shown), the elastic body seat 71 has a plurality of countersunk screw holes 72 (as shown in FIG. Figure 5 and Figure 7 As shown in the figure, these elastomers 73 are arranged between these recessed holes 64 and these countersunk screw holes 72 in a one-to-one manner, one end of these elastomers 73 abuts against the elastomer seat 71 as a support, and the other end of these elastomers 73 abuts against the pressure ring 60 to provide elastic force to push the pressure ring 60 toward the brake ring 50; these pins 74 are passed through these elastomers 73 in a one-to-one manner and are screwed into these countersunk screw holes 72 to provide a supporting effect for these elastomers 73.

[0083] In actual operation, the second fluid 24 is introduced into the second flow channel 34 by using the second joint 18, so that the second fluid 24 enters the second chamber 63. Figure 9As shown, on one hand, the second fluid 24 will push the brake ring 50 to keep the brake ring 50 in the braking position P1 as shown in Figure 9 . On the other hand, the second fluid 24 will push the pressure ring 60 to compress these elastomers 73. Since the second chamber 63 is in a sealed state, and the force exerted by the second fluid 24 on the pressure ring 60 and the force exerted by these elastomers 73 on the pressure ring 60 are in opposite directions, according to Pascal's principle, the energy generated by the compression of these elastomers 73 will act on the brake ring 50 via the second fluid 24, enabling the brake ring 50 to achieve a double supercharging effect. That is, when the second fluid 24 is introduced into the second chamber 63, Ft = F1 + F2, where Ft is the total braking force provided by the brake ring 50, F1 is the thrust exerted by the second fluid 24 on the brake ring 50, and F2 is the energy generated when all the elastomers 73 are compressed. If the force exerted by the second fluid 24 on the pressure ring 60 is greater, the energy generated by the compression of these elastomers 73 will also be greater. Therefore, the total braking force that the brake ring 50 can provide will also be greater.

[0084] Conversely, when the rotating shaft 12 needs to operate normally, first stop introducing the second fluid 24 into the second chamber 63, and then use the first joint 16 to introduce the first fluid 22 into the first flow channel 33, so that the first fluid 22 enters the first chamber 54, as shown in Figure 10 . The first fluid 22 will push the brake ring 50, and then the brake ring 50 will push the pressure ring 60. Since these elastomers 73 still exert a force on the pressure ring 60 at this time, when the force exerted by the first fluid 22 on the brake ring 50 is greater than the force exerted by these elastomers 73 on the pressure ring 60, the brake ring 50 can be kept in the braking release position P2 as shown in Figure 10 . At this time, the rotating disc 44 will not be clamped by the first fixed disc 41 and the second fixed disc 42, so the rotating shaft 12 can operate normally.

[0085] Once the supply of the second fluid 24 fails due to special circumstances (such as a sudden power outage or a pipeline rupture), although the brake ring 50 will lose the thrust provided by the second fluid 24, these elastomers 73 can still exert a force on the brake ring 50 through the pressure ring 60 to keep the brake ring 50 in the braking position P1 as shown in Figure 7 , enabling the rotating shaft 12 to achieve the effect of safe shutdown. In other words, under normal circumstances, the brake ring 50 will use the force of the second fluid 24 and the force generated when these elastomers 73 are compressed to provide a complete braking force for the rotating disc 44. If the supply of the second fluid 24 fails, the partial braking force provided by these elastomers 73 can still keep the brake ring 50 in the position as shown in Figure 7The shown braking position P1 thus achieves the effect of normally closed braking, thereby enhancing the safety in operation.

[0086] In addition, it should be supplemented and explained that, as Figure 11 shown, the braking portion 52 of the braking ring 50 has a braking surface 53 for pressing against the first fixed disc 41. The radial length L of the braking surface 53 does not exceed the overlapping area of the first fixed disc 41, the second fixed disc 42, and the rotating disc 44. If the radial length L of the braking surface 53 exceeds the aforementioned range, in addition to possibly pressing on the rotating disc 44 and causing damage to the rotating disc 44, it may also press on the spacer ring 43 and affect the braking effect. Again, as Figure 12 shown, the braking surface 53 is adjacent to the inner ring surface 51 and has a first included angle θ1 less than 90 degrees with the inner ring surface 51. If the first included angle θ1 is greater than or equal to 90 degrees, it may cause the first fixed disc 41 to be deformed into a shape similar to an S state after being pressed down by the braking surface 53, making the first fixed disc 41 have two bending points. This state belongs to the shear effect and makes it difficult to return to its original state. Thus, it is likely to affect the movement of the rotating disc 44 in the braking release state. When the first included angle θ1 is less than 90 degrees, the first included angle θ1 approaches the deformation angle of the first fixed disc 41, making the first fixed disc 41 have only one bending point, which can effectively improve the influence of the shear force on the service life of the first fixed disc 41. In addition, the first fixed disc 41 has a pressed section 412 pressed by the braking surface 53. There is a second included angle θ2 between the pressed section 412 of the first fixed disc 41 and the inner ring surface 51 of the braking ring 50, and the second included angle θ2 is less than or equal to the first included angle θ1. Through the design of the aforementioned special angles, on the one hand, the best clamping effect can be obtained, and on the other hand, the first fixed disc 41 can smoothly return to its original state in the braking release state, so as to extend the service life of the first fixed disc 41.

[0087] In summary, the normally closed brake 20 of the present invention utilizes the design of the first chamber 54 and the second chamber 63 in combination with the braking ring 50 and the pressure ring 60. As long as the first fluid 22 and the second fluid 24 are respectively introduced into the first chamber 54 and the second chamber 63, the braking ring 50 can be controlled to provide a braking release effect and a braking effect on the rotating disc 44. In addition, in the situation where the first fluid 22 is not introduced into the first chamber 54 and the second fluid 24 is not introduced into the second chamber 63 (or the supply of the second fluid 24 fails), through the partial braking force provided by these elastomers 73, the braking ring 50 can still be maintained at the braking position P1 to achieve the effect of normally closed braking, thereby enhancing the safety in operation. Therefore, it is applicable to the occasions of heavy cutting and high feed.

[0088] The specific embodiments described above further elaborate on the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only for the specific embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A normally closed braking device, comprising: A housing having a receiving groove; A disc set disposed in the receiving groove of the housing and having a first fixed disc, a second fixed disc and a rotating disc, the rotating disc being disposed between the first fixed disc and the second fixed disc; A braking ring movably disposed in the receiving groove of the housing and forming a first chamber with the housing, the braking ring having a braking portion, when the braking ring is in a braking position, the braking portion of the braking ring presses against the first fixed disc, so that the rotating disc is fixed between the first fixed disc and the second fixed disc, when the braking ring is in a braking release position, the braking portion of the braking ring releases the first fixed disc, so that the rotating disc can rotate relative to the first fixed disc and the second fixed disc; A pressure ring disposed in the receiving groove of the housing and partially abutting against the braking ring, so that a second chamber is formed between the pressure ring and the braking ring; and An elastic unit disposed on the pressure ring for pushing the pressure ring towards the braking ring; Among them, When only a fluid is introduced into the first chamber, the braking ring is held in a braking release position by the action of the fluid, when only the fluid is introduced into the second chamber, the braking ring is held in the braking position by the action of the fluid, and the pressure ring compresses the elastic unit by the action of the fluid, the direction of the force exerted by the fluid on the pressure ring is opposite to the direction of the force exerted by the elastic unit on the pressure ring, when the fluid is not introduced into the first chamber and the second chamber, the pressure ring is pushed by the force exerted by the elastic unit to push the braking ring, so that the braking ring is held in the braking position; Wherein, the braking portion of the braking ring has a braking surface, when the braking ring is in the braking position, the braking ring presses against the first fixed disc with the braking surface of the braking portion, the braking ring further has an inner ring surface adjacent to the braking surface, and a first included angle is formed between the braking surface and the inner ring surface, and the first included angle is less than 90 degrees.

2. The normally closed braking device according to claim 1, wherein, The braking ring has an inner ring surface, a sealing ring and a back-up ring adjacent to the sealing ring are embedded in the inner ring surface, a first flange and a second flange adjacent to the first flange are provided on one side of the pressure ring facing the braking ring, the first flange of the pressure ring abuts against the braking ring, and the second flange of the pressure ring abuts against the sealing ring and the back-up ring.

3. The normally-closed braking device according to claim 1, wherein, The braking portion of the braking ring has a braking surface, when the braking ring is in the braking position, the braking ring presses against the first fixed disc with the braking surface of the braking portion, and the radial length of the braking surface does not exceed the overlapping area of the first fixed disc, the second fixed disc and the rotating disc.

4. The normally-closed braking device according to claim 1, wherein, The first fixed disc has a compressed section, when the braking ring is in the braking position, the braking ring presses against the compressed section of the first fixed disc with the braking surface of the braking portion, and a second included angle is formed between the compressed section of the first fixed disc and the inner ring surface of the braking ring, and the second included angle is less than or equal to the first included angle.

5. The normally-closed braking device according to claim 1, wherein, The elastic unit has an elastic body seat and a plurality of elastic bodies. The elastic body seats are arranged in the accommodating groove of the housing and adjacent to the pressing ring. The elastic bodies are arranged between the pressing ring and the elastic body seats to push the pressing ring towards the braking ring.

6. A rotary worktable, comprising: A normally closed braking device as described in any one of claims 1 to 5; and A rotating shaft rotatably arranged in the accommodating groove of the housing, and the outer peripheral surface of the rotating shaft is fixedly connected to the rotating disc so that the rotating shaft can act synchronously with the rotating disc.

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