Ultrasonic knife with hitting function and blade head

Abstract

The application discloses an ultrasonic knife with a hitting function and a knife head, which comprises a connecting part, a transition part and a cutting part connected in sequence, symmetrical cutting surfaces are arranged on both sides of the front end of the transition part, the thickness of the transition part is gradually thinned, the transition part and the cutting part are not located on the same axis, a bent supporting part is formed at the connection between the cutting part and the transition part, the top of the supporting part is higher than the transition part, a cutting surface is formed on the side opposite to the supporting part of the cutting part, the cutting surface extends forward in an arc shape away from the longitudinal axis of the transition part, and the cutting surface makes longitudinal vibration while making transverse vibration. The connecting part between the cutting part and the transition part is bent, so that the cutting surface at the front end of the cutting part makes transverse vibration while making longitudinal vibration, transverse hitting is formed on the bone tissue adjacent to the cutting surface, the cutting efficiency is greatly improved, and the visual field range of the operation is increased.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic cutting tool technology, and more specifically to an ultrasonic scalpel and cutting head with a striking function. Background Technology

[0002] In current orthopedic surgeries, ultrasonic cutting with a osteotome is commonly used. A conventional osteotome has a rod-like structure, symmetrical from distal to proximal, with the cutting edge formed at the proximal end. In actual use, the sides of this cutting edge are relatively smooth. During bone cutting, the cutting edge wall tends to adhere closely to the bone tissue, creating excessive friction. This requires the osteotome to apply significant pressure during cutting, posing a risk during surgery. Furthermore, the cutting edge of the osteotome is typically quite thin, making it prone to breakage under excessive pressure. This also leads to substantial bone loss, complicating the patient's subsequent rehabilitation. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide an ultrasonic scalpel and scalpel head with a striking function.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] An ultrasonic scalpel with a striking function includes a connecting part, a transition part, and a cutting part connected in sequence. The front end of the transition part has symmetrical cut surfaces on both sides, making the thickness of the transition part gradually thinner. The transition part and the cutting part are not located on the same axis, and a bent support part is formed at the connection between the cutting part and the transition part. The top of the support part is higher than the transition part. The side of the cutting part opposite to the support part forms a cutting surface. The cutting surface extends forward in an arc shape away from the longitudinal axis of the transition part. When the cutting part vibrates longitudinally, the cutting surface generates a transverse vibration perpendicular to the longitudinal vibration.

[0006] Preferably, the side of the cutting part opposite to the cutting surface also extends in an arc shape, and the width of the cutting part gradually decreases from its tail end to its front end, and the front end of the cutting part is an arc-shaped side.

[0007] Preferably, the cutting surface has a straight, extending transverse vibrating portion near the front end, and the length of the transverse vibrating portion does not exceed one-half the length of the cutting surface.

[0008] Preferably, the lateral vibration amplitude of the transverse vibration section does not exceed 1.5 times the longitudinal vibration amplitude of the cutting section.

[0009] Preferably, a set of serrations is provided on the cutting surface, and the serrations extend obliquely towards the front end of the cutting portion in an asymmetrical formation.

[0010] Preferably, the tilt angle α of the first side of the saw tooth is greater than the tilt angle β of the second side.

[0011] Preferably, the cutting part has grooves of matching shape on the end faces on both sides of the cutting surface, and the two grooves are respectively connected to the two cutting surfaces, and the surface of the groove does not protrude outward from the cutting surface.

[0012] Preferably, a set of flow channels with the same extension direction as the saw teeth are provided on the cutting surface, and the surface of the flow channels does not protrude beyond the surface of the groove, so that the groove can communicate with the outside through the flow channels.

[0013] Preferably, a flow channel is provided every three of the saw teeth.

[0014] Preferably, the saw teeth are spaced apart from each other, and the spaced apart forms a third angle ε with the longitudinal axis of the cutting surface, wherein the third angle ε is greater than 0° and less than or equal to 90°.

[0015] Preferably, a concave balancing portion is formed at the connection between the cutting portion and the transition portion on opposite sides of the support portion.

[0016] An ultrasonic scalpel tip includes a thin-bladed cutting section, wherein at least one side of the cutting section has a set of serrations, and the inclination angle α of the first side of the serrations is greater than the inclination angle β of the second side.

[0017] Preferably, the tilt angle β is in the range of 20°-100°, and the difference between it and the tilt angle α is between 50°-60°.

[0018] Preferably, the cutting portion has a bent support portion that extends obliquely from the support portion in an axial direction offset from its tail end.

[0019] Preferably, grooves are provided on both end faces of the cutting part, and the distance between the outer edge of the groove and the outer edge of the cutting part is between 0.2 and 0.8 mm.

[0020] Preferably, a flow channel communicating with the outside is provided every three serrations, and the depth of the flow channel is not less than that of the groove.

[0021] Preferably, the tilt angle β is 40°.

[0022] Preferably, the saw teeth are spaced apart from each other, and the spaced apart forms a third angle ε with the longitudinal axis of the cutting part, wherein the third angle ε is greater than 0° and less than or equal to 90°.

[0023] The beneficial effects of this invention are mainly reflected in:

[0024] 1. The connection between the cutting part and the transition part is bent to form an upwardly convex support part and to make the cutting part extend in an arc away from the axis of the transition part, so that the front end of the cutting part is furthest away from the axis of the transition part. When the cutting part vibrates longitudinally, the cutting surface at its front end vibrates laterally, and the lateral vibration forms a lateral impact on the adjacent bone tissue during cutting, which greatly improves the cutting efficiency and increases the field of vision for surgery.

[0025] 2. The upward-convex support portion is higher than the side of the transition portion, which allows the surrounding tissue to be shielded during surgery, expands the surgical field of view at the cutting site, and is conducive to bone cutting. At the same time, the cutting portion is tilted off the axis of the transition portion, which further increases the distance between the front end of the cutting portion and the apex of the support portion, thus increasing the surgical field of view.

[0026] 3. Grooves are provided on both sides of the cutting part to guide cooling water, and flow channels are provided on the grooves to ensure that the cooling water flows to the cutting part in time to cool it down in real time and protect the cell activity at the cutting part. Attached Figure Description

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings:

[0028] Figure 1 : A schematic diagram of an embodiment of the present invention;

[0029] Figure 2 : Partial schematic diagram of an embodiment of the present invention;

[0030] Figure 3 : Partial schematic diagram of a preferred embodiment of the present invention;

[0031] Figure 4 : Partial schematic diagram of an embodiment of the present invention;

[0032] Figure 5 : Partial schematic diagram of an embodiment of the present invention;

[0033] Figure 6 : Partial schematic diagram of an embodiment of the present invention;

[0034] Figure 7 : Partial schematic diagram of an embodiment of the present invention;

[0035] Figure 8 : Partial schematic diagram of an embodiment of the present invention;

[0036] Figure 9 Distribution diagram of total number of teeth and number of teeth vibrating laterally as a function of tilt angle β;

[0037] Figure 10 : Partial schematic diagram of an embodiment of the present invention;

[0038] Figure 11 : Partial schematic diagram of an embodiment of the present invention. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments are not limited to the present invention, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.

[0040] In the description of the solution, it should be noted that the terms "center," "upper," "lower," "left," "right," "front," "rear," "vertical," "horizontal," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience and simplification of description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Also, in the description of the solution, with the operator as a reference, the direction closer to the operator is the proximal end, and the direction farther from the operator is the distal end.

[0041] like Figures 1 to 11 As shown, this invention discloses an ultrasonic scalpel with a striking function, comprising a connecting part 1, a transition part 3, and a cutting part 4 connected in sequence. The front end of the transition part 3 is symmetrically provided with cut surfaces 31 on both sides, so that the thickness of the transition part 3 gradually decreases. The transition part 3 and the cutting part 4 are not located on the same axis, and a bent support part 43 is formed at the connection between the cutting part 4 and the transition part 3. The top of the support part 43 is higher than the transition part 3. A cutting surface 40 is formed on the side of the cutting part 4 opposite to the support part 43. The cutting surface 40 extends forward in an arc shape away from the longitudinal axis of the transition part 3. When the cutting part 4 vibrates longitudinally, the cutting surface 40 generates a transverse vibration perpendicular to the longitudinal vibration.

[0042] This invention features a bent connection between the cutting section 4 and the transition section 3. This bend forms an upwardly convex support section 43, higher than the side of the transition section 3, which shields surrounding tissue during surgery, expanding the surgical field of view and facilitating bone cutting. Simultaneously, the cutting section 4 extends in an arc away from the axis of the transition section, maximizing the distance between its front end and the axis of the transition section 3. When the cutting section 4 is energized and vibrates longitudinally, its cutting surface 40 vibrates laterally, creating a lateral impact on adjacent bone tissue during cutting, significantly improving cutting efficiency and increasing the surgical field of view. Furthermore, the offset of the cutting section 4 from the axis of the transition section 3 further increases the distance between the front end of the cutting section 4 and the apex of the support section 43, further expanding the surgical field of view.

[0043] Specifically, the connecting portion is a tubular structure with a slightly larger diameter than the transition portion 3, used to connect the handheld component. The transition portion 3 is formed by connecting a cylinder and a sheet. The side of the cutting portion 4 opposite to the cutting surface 40 also extends in an arc shape, and the width of the cutting portion 4 gradually decreases from its tail end to its front end, with the front end of the cutting portion 4 having an arc-shaped side. The arc-shaped extension of the cutting surface 40 increases its extension distance without changing the vertical distance between its front and rear ends. The gradual reduction in the width of the cutting portion 4 is beneficial for meeting the needs of cuts with different diameters, increasing its flexibility of use. In other feasible embodiments, the width of the cutting portion 4 can also remain constant.

[0044] Further such as Figure 4 As shown, the cutting surface 40 has a straight, extending transverse vibration portion 401 near its front end. The length of the transverse vibration portion 401 does not exceed half the length of the cutting surface 40. In a preferred embodiment, the length of the transverse vibration portion 40 is preferably one-quarter of the total length of the cutting surface 40. The saw teeth 41 that can generate transverse vibration are the number of transverse vibration teeth. To ensure sufficient transverse vibration driving force, the number of transverse vibration teeth is not less than three, and the number of saw teeth 41 at the transverse vibration portion 401 is not less than three.

[0045] In this design, the transverse vibration amplitude of the transverse vibration section 401 does not exceed 2.5 times the longitudinal vibration amplitude of the cutting section 4, so that the cutting effect between transverse and longitudinal vibration is optimal when the total amplitude is constant.

[0046] Furthermore, the cutting surface 40 can be formed into a cutting edge of any structure. In a preferred embodiment, the cutting surface 40 is provided with a set of serrations 41. The thickness of the serrations 41 extends from thick to thin, and the ratio of the thickness of the thinnest part of the serration 41 to the thickness of the thickest part is between 0.5 and 0.8. The thickness of the thickest part is between 0.7 mm and 1.2 mm, and the thickness of the thickest part does not exceed 1 mm, preferably between 0.8 mm and 1.0 mm. This structural arrangement allows the serrations 41 to gradually extend from thick to thin, with relatively sharp edges and high cutting force. The thicker parts can also increase its overall rigidity, making it less prone to breakage. Moreover, the overall thinness of the serrations 41 results in less bone loss during cutting, which is beneficial to the patient's later rehabilitation.

[0047] like Figure 2 As shown, a concave balancing portion 44 is formed at the connection between the cutting portion 4 and the transition portion 3 on opposite sides of the support portion 43. Since the extending direction of the cutting portion 4 is away from the axis of the transition portion 3, the center of the cutting portion 4 shifts downward. The balancing portion 44 balances the center of gravity of the entire tool tip, improving the user's handling. Preferably, the balancing portion 44 has a concave structure, forming a gap B3 between it and the side of the transition portion 3. Figure 10 As shown. In other feasible embodiments, the balancing portion 44 may also be a plane that is directly connected to the side of the transition portion 3.

[0048] like Figure 5 As shown, the serrations 41 extend asymmetrically towards the front end near the cutting portion 4. Specifically, the inclination angle α of the first side 411 of the serration 41 is greater than the inclination angle β of its second side 412. The difference between the inclination angles α and β is between 50° and 60°, and the angle β ranges from 20° to 100°, preferably 40°. The inconsistent inclination angles of the first side 411 and the second side 412 of the serration 41 in this design result in an asymmetrical structure. This structure maximizes the number of transverse teeth to enhance rigidity, making the serrations 41 less prone to breakage during cutting and ensuring smooth and efficient cutting.

[0049] The difference between the tilt angle β and the tilt angle α is the gap angle between each pair of saw teeth 41. When the difference is too large, the gap between the saw teeth 41 is too large, which will reduce cutting efficiency; when the difference is too small, the gap between the saw teeth 41 is too small, and the distribution is too dense, which will increase the contact area between them and the bone tissue, requiring more pressure, and easily causing the saw teeth 41 to break. Figure 9The diagram shows the distribution of the total number of teeth and the number of transverse vibration teeth of the saw teeth 41 while maintaining the vibration amplitude. The distribution is symmetrical when the second included angle β = 60°. Furthermore, to conform to the user's operating inertia, the tips of the saw teeth 41 are preferably inclined towards the front end of the cutting part 4. The inclination angle β is preferably between 20° and 60°. Based on the selection of the optimal number of transverse vibration teeth, the inclination angle β in the optimal embodiment is calculated to be 40°.

[0050] like Figure 2-5 As shown, the cutting part 4 has grooves 42 of matching shape on both sides of the cutting surface 40, and the two grooves 42 are respectively connected to the two cutting surfaces 31. The surface of the groove 42 does not protrude from the cutting surface 31 to ensure smooth flow of cooling water. In another feasible embodiment, the groove 42 may have a connecting groove 32 on the cutting surface 31 to increase the volume of the groove 42. The distance between the outer edge of the groove 42 and the outer edge of the cutting part 4 is between 0.2-0.8 mm to ensure sufficient cutting rigidity, reduce jamming, and ensure smooth cutting.

[0051] Further such as Figure 3 As shown, a set of flow channels 421 extending in the same direction as the saw teeth 41 are provided on the cutting surface 40. The surface of the flow channels 421 does not protrude beyond the surface of the groove 42, allowing the groove 42 to communicate with the outside through the flow channels 421. The flow channels 421 facilitate the timely outflow of cooling water.

[0052] The flow channel 421 in this solution can be configured in various ways, and the serrations 41 can be arranged at arbitrary intervals. To maximize the conservation of cooling water and avoid waste and unnecessary increases in surgical costs, in this preferred embodiment, a flow channel 421 is provided every three serrations 41. This arrangement is because the heat generated during bone cutting is primarily due to frictional heat generated between the serrations 41 and the bone tissue during vibration. Based on this, a heat model of the heat generated per unit time during bone cutting is established using different vibration speeds of the serration tips 41, where the internal stress heat of the osteotome is negligible.

[0053] Total heat generated per unit time during bone cutting: W = 2 μN·A m ·f,

[0054] Where A m : Amplitude of the blade tip; f: Working frequency of the ultrasonic bone dynamics system; μ: Coefficient of friction between the blade tip and bone tissue; N: Vertical pressure of the blade tip on the bone tissue.

[0055] Since the total heat generated by friction will raise the temperature of bone tissue, the initial temperature of bone tissue is the same as the body temperature, and the maximum temperature is the highest temperature at which bone tissue can maintain its biological activity. The maximum allowable heat per unit time to ensure the biological activity of bone tissue is as follows:

[0056] W1 = c b m b (T2-T1)

[0057] Where c b Specific heat capacity of bone tissue; m b : Bone tissue quality involved in heat exchange; T1: Human body temperature; T2: The highest temperature at which bone tissue maintains biological activity.

[0058] If the heat generated by friction is much higher than the maximum allowable heat absorption of bone tissue, the remaining heat needs to be absorbed by cooling water. The highest permissible temperature of the cooling water is the lowest temperature at which various human tissues that the cooling water comes into contact with maintain biological activity; this temperature is the highest temperature at which bone tissue maintains biological activity. Based on the heat consumed by the cooling water, the required volume of cooling water can be calculated, and thus the cooling water flow rate can be determined.

[0059] Calculate m based on the amount of heat that the cooling water needs to remove per unit time. w In order to save cooling water as much as possible.

[0060] ΔW=W-W1

[0061] ΔW=c w m w (T2-T0)

[0062] Where: c w Specific heat capacity of physiological saline; m w : Minimum mass of physiological saline required for cooling; T0: Room temperature; T2: Maximum temperature at which bone tissue retains biological activity.

[0063] Based on the calculated m w To find the minimum volume of cooling water required per unit time, i.e., the cooling water flow rate V′:

[0064] V′=m w / ρ

[0065] Where: ρ: density of physiological saline.

[0066] Considering that the cooling water is in a cavitation state during cutting operations, and the thermal effect of water in the cavitation state is lower than that of water under normal conditions, the actual required cooling water flow rate V is:

[0067] V = V′ / A

[0068] Where: A is the cavitation hydrothermal effect coefficient, which is generally 70-80% according to relevant literature, and preferably 75% in this embodiment.

[0069] In this design, the osteotome is fitted with a protective sleeve. Cooling water flows through the gap between the protective sleeve and the osteotome, and is released at the end of the protective sleeve. The flow velocity v of the cooling water exiting the protective sleeve can be obtained from the cross-sectional area of ​​the gap. w :

[0070] v w =V / ΔS

[0071] Where ΔS is the difference between the cross-sectional area of ​​the protective sleeve at the cooling water outlet and the cross-sectional area of ​​the cutter head.

[0072] like Figure 8 As shown, due to the presence of the flow channel 421, cooling water flows from the flow channel 421 to the serration 41 to quickly reach the surgical site, and flows downwards under the influence of weight g. The length Wh1 between the start and end points of the flow channel 421 is Wh1 = g·t′. 2 / 2, to find t′.

[0073] During time t′, the cooling water flows at a rate of v. w The flow moves axially to the head end, and the distance Wh2 it moves is Wh2 = v w ·t′, calculate the distance Wh2 that was moved.

[0074] The calculation results show that Wh2:Wh1≈3, meaning the ratio between the axial movement distance of the cooling water and its radial flow distance is 3. In this scheme, the width and length of a single sawtooth 41 are approximately equal to 1:1. Therefore, the ratio of the number of sawtooth 41 to the number of flow channels 421 is 3:1. That is, one flow channel 421 is set every three sawtooth 41s. This allows the cooling water with the smallest volume to meet the cooling requirements, thereby saving cooling water usage as much as possible and avoiding waste or obstruction of surgery caused by the use of a large amount of cooling water, which would unnecessarily increase the cost of surgery.

[0075] like Figure 6 , 7 As shown, the saw teeth 41 are spaced 413 apart, and the spaced 413 forms a third angle ε with the longitudinal axis of the cutting surface 40. The third angle ε is greater than 0° and less than or equal to 90°, and the third angle ε is preferably 90°, so as to maximize the cutting efficiency.

[0076] like Figure 11As shown, the distance B6 from the vertex of the support portion 43 to the front end of the cutting portion 4 is between 15-20 mm. The two sides of the support portion 43 have an asymmetrical structure, and the projected lengths B71 and B72 on both sides do not exceed 5 mm. The maximum gap width B4 between the vertex of the support portion 43 and the front end of the cutting portion 4 is greater than the diameter B1 of the fixed arm 3. The maximum distance B5 between the front end of the cutting portion 4 and the side of the transition portion 3 is not less than 1 mm.

[0077] In addition, a wrench position 2 is provided on the connecting part 1.

[0078] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0079] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. An ultrasonic scalpel with a striking function, comprising a connecting part (1), a transition part (3), and a cutting part (4) connected in sequence, characterized in that: The transition section (3) has symmetrical cut surfaces (31) on both sides of its front end, which makes the thickness of the transition section (3) gradually thin. The transition section (3) and the cutting section (4) are not located on the same axis. A bent support section (43) is formed at the connection between the cutting section (4) and the transition section (3). The top of the support section (43) is higher than the transition section (3). A cutting surface (40) is formed on the side opposite to the support section (43) of the cutting section (4). The cutting surface (40) extends forward in an arc away from the longitudinal axis of the transition section (3). The cutting surface (40) vibrates longitudinally and laterally at the same time. The cutting surface (40) has a straight transverse vibration section (401) near the front end. The length of the transverse vibration section (401) is no more than half the length of the cutting surface (40). The side of the cutting part (4) opposite to the cutting surface (40) also extends forward in an arc shape, and the width of the cutting part (4) gradually decreases from its tail end to its front end. The front end of the cutting part (4) is an arc side. The transverse vibration amplitude of the transverse vibration section (401) does not exceed 2.5 times the longitudinal vibration amplitude of the cutting section (4); A set of serrations (41) are provided on the cutting surface (40), and the serrations (41) extend obliquely toward the front end of the cutting part (4) in an asymmetrical formation. A concave balancing portion (44) is formed at the connection between the cutting portion (4) and the transition portion (3) on opposite sides of the support portion (43).

2. The ultrasonic scalpel with striking function according to claim 1, characterized in that: The tilt angle α of the first side (411) of the sawtooth (41) is greater than the tilt angle β of its second side (412).

3. The ultrasonic scalpel with striking function according to claim 2, characterized in that: The cutting part (4) is provided with a groove (42) matching the shape on at least one side of the cutting surface (40), and the groove (42) is connected to the cutting surface (31) respectively, and the surface of the groove (42) does not protrude outward from the cutting surface (31).

4. The ultrasonic scalpel with striking function according to claim 3, characterized in that: A set of flow channels (421) with the same extension direction as the saw teeth (41) are provided on the cutting surface (40). The surface of the flow channel (421) does not protrude outward from the surface of the groove (42), so that the groove (42) can communicate with the outside through the flow channel (421).

5. The ultrasonic scalpel with striking function according to claim 4, characterized in that: A flow channel (421) is provided every three said saw teeth (41).

6. The ultrasonic scalpel with striking function according to claim 5, characterized in that: The saw teeth (41) are spaced apart by a gap (413), and the gap (413) forms a third included angle ε with the longitudinal axis of the cutting surface (40), the third included angle ε being greater than 0° and less than or equal to 90°.

7. A blade tip for use in the ultrasonic scalpel with striking function as described in claim 1, characterized in that: It includes a thin-sheet cutting part (4), which has a set of serrations (41) on at least one side, and the inclination angle α of the first side (411) of the serrations (41) is greater than the inclination angle β of the second side (412).

8. The ultrasonic scalpel tip according to claim 7, characterized in that: The tilt angle β has an angle range of 20°-100°, and the difference between it and the tilt angle α is between 50°-60°.

9. The ultrasonic scalpel tip according to claim 7, characterized in that: The cutting part (4) has a bent support part (43) that extends obliquely from the support part (43) in a direction away from its tail end.

10. The ultrasonic scalpel tip according to claim 7, characterized in that: The cutting part (4) has grooves (42) on both end faces, and the distance between the outer edge of the groove (42) and the outer edge of the cutting part (4) is between 0.2-0.8 mm.

11. The ultrasonic scalpel tip according to claim 10, characterized in that: A flow channel (421) communicating with the outside is provided every three of the saw teeth (41), and the depth of the flow channel (421) is not less than that of the groove (42).

12. The blade of an ultrasonic scalpel according to any one of claims 7, 9, 10 and 11, characterized in that: The tilt angle β is 40°.

13. The ultrasonic scalpel tip according to claim 7, characterized in that: The saw teeth (41) are spaced apart by a gap (413), and the gap (413) forms a third included angle ε with the longitudinal axis of the cutting surface (40), the third included angle ε being greater than 0° and less than or equal to 90°.

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