Vibration motor
By designing a vibration motor composed of a stator, elastic element, and mover, the problems of large size and complex structure of existing vibration devices have been solved, achieving miniaturized, easy-to-assemble, and low-cost vibration effects, and providing a powerful vibration experience.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- AAC MICROTECH (CHANGZHOU) CO LTD
- Filing Date
- 2025-01-06
- Publication Date
- 2026-07-09
AI Technical Summary
Existing vibration devices are large in size, complex in structure, and cumbersome to assemble, making them difficult to apply in applications with high cost and performance requirements.
A vibration motor comprising a stator, an elastic element, and a mover is designed. The stator consists of a housing and a magnet assembly. The mover is suspended in a housing space by the elastic element. The mover includes an iron core unit and windings. The windings are located between the iron cores. The magnets are magnetized in a specific direction to generate an electromagnetic resultant force to drive the vibration.
This invention achieves a vibration motor that is small in size, simple in structure, and easy to assemble, reducing production costs and providing a powerful vibration experience in a small volume, with fast response and realistic vibration.
Smart Images
Figure CN2025070671_09072026_PF_FP_ABST
Abstract
Description
A vibration motor Technical Field
[0001] This application relates to the field of vibration devices, specifically to a vibration motor. Background Technology
[0002] In the existing technology, the most common vibration device is the X-axis linear motor. This type of motor is not only large in size, but also has a complex structure, is cumbersome to assemble, and has high production costs, making it difficult to apply in some applications where both cost and performance are required.
[0003] Therefore, it is necessary to provide a vibration motor that is small in size, simple in structure, and easy to assemble. Technical issues
[0004] The purpose of this application is to provide a vibration motor that solves the technical problems of large size, complex structure and cumbersome assembly of existing vibration devices. Technical solutions
[0005] The technical solution of this application is as follows:
[0006] This application provides a vibration motor, including: a stator, an elastic element, and a mover that vibrates along a first direction;
[0007] The stator includes a housing with a receiving space and a magnet assembly housed within the receiving space. The magnet assembly includes two first magnets and two second magnets. The two first magnets are spaced apart and symmetrically fixed to the housing in a second direction, and the two second magnets are spaced apart and symmetrically fixed to the housing in a third direction. The first direction, the second direction, and the third direction are perpendicular to each other.
[0008] The mover is suspended in the receiving space at both ends of the first direction by the elastic element. The mover includes an iron core unit and a winding. The iron core unit includes a first iron core and a second iron core and a third iron core symmetrically fixed at both ends of the first iron core in the first direction. The winding is wound around the first iron core and located between the second iron core and the third iron core.
[0009] Preferably, the winding is arranged around the first direction;
[0010] The two first magnets are respectively magnetized along the second direction and their magnetization directions are opposite. The first magnet includes a first magnetized region and a second magnetized region symmetrically disposed at both ends of the first magnetized region in the first direction. The magnetization direction of the second magnetized region is opposite to that of the first magnetized region.
[0011] The two second magnets are magnetized along the third direction respectively, and their magnetization directions are opposite.
[0012] Preferably, the second magnet includes a third magnetized region and a fourth magnetized region symmetrically disposed at both ends of the third magnetized region in the first direction, wherein the magnetization direction of the fourth magnetized region is opposite to that of the third magnetized region.
[0013] Preferably, the outer shell is a hollow structure with two openings, the two openings being arranged opposite each other in the first direction, and the hollow portion of the outer shell is configured as the receiving space;
[0014] The vibration motor includes two elastic elements, each corresponding to one of the openings. The two ends of the elastic elements are fixed to the outer shell, so that each elastic element spans across the corresponding opening.
[0015] Preferably, the length of the housing in the second direction is less than the length of the housing in the third direction, and the housing includes two first surfaces spaced apart in the second direction and two second surfaces spaced apart in the third direction, the two first surfaces and the two second surfaces surrounding the receiving space;
[0016] The first magnet is fixed to the first surface;
[0017] There is a gap between the second magnet and the second surface;
[0018] The elastic element is fixed to the outer shell at both ends in the third direction.
[0019] Preferably, the stator further includes two pole cores housed within the housing space, the two pole cores being spaced apart in the third direction and symmetrically fixed to the outer shell, and a gap being formed between the pole cores and the second surface;
[0020] Two second magnets are disposed between the two pole cores and are respectively fixed to the corresponding pole cores.
[0021] Preferably, the elastic element has a through hole;
[0022] The first iron core includes a first iron core body, a first protrusion extending from the first iron core body along the first direction toward the second iron core and connecting to the second iron core, and a second protrusion extending from the first iron core body along the first direction toward the third iron core and connecting to the third iron core. The first protrusion and the second protrusion are symmetrically arranged in the first direction, and the first protrusion and the second protrusion are respectively inserted into the through hole of the corresponding elastic member.
[0023] Preferably, the second iron core has a first insertion hole that engages with the first protrusion, and the third iron core has a second insertion hole that engages with the second protrusion.
[0024] Preferably, at least one of the first iron core, the second iron core, and the third iron core is formed by stacking multiple layers of iron sheets. Beneficial effects
[0025] The beneficial effects of this application are as follows: The vibration motor of this application includes a stator, an elastic element, and a mover that vibrates along a first direction; the stator includes a housing with a receiving space and a magnet assembly housed within the receiving space, the magnet assembly including two first magnets and two second magnets, wherein the two first magnets are spaced apart and symmetrically fixed to the housing in a second direction, and the two second magnets are spaced apart and symmetrically fixed to the housing in a third direction, the first direction, the second direction, and the third direction being perpendicular to each other; the mover is suspended in the receiving space at both ends of the first direction by the elastic element, and the mover includes an iron core unit and a winding. The core unit includes a first core and a second and a third core symmetrically fixed at both ends of the first core in a first direction. The winding is wound around the first core and located between the second and third cores. It is not only simple in structure and small in size, easy to assemble, reducing production requirements and costs, but also has high space utilization, providing a more powerful vibration experience in a smaller volume. When a periodic current is passed through the winding, the mover is subjected to a periodic electromagnetic resultant force. This resultant force acts as an excitation source to drive the direct-drive vibration system composed of the mover, stator and elastic components to vibrate, resulting in a fast response and a more realistic vibration sensation. Attached Figure Description
[0026] Figure 1 is a schematic diagram of the structure of the vibration motor of this application.
[0027] Figure 2 is a schematic diagram of a partial structure of the vibration motor shown in Figure 1.
[0028] Figure 3 is an exploded view of the vibration motor shown in Figure 1.
[0029] Figure 4 is a top view of the vibration motor shown in Figure 1.
[0030] Figure 5 is an enlarged view of the AA cross-sectional structure in Figure 4.
[0031] Figure 6 is an enlarged view of the BB cross-sectional structure in Figure 4.
[0032] Figure 7 is a schematic diagram of the magnetization direction of the first magnet in the vibration motor shown in Figure 1.
[0033] Figure 8 is a schematic diagram of the first magnetization direction of the second magnet in the vibration motor shown in Figure 1.
[0034] Figure 9 is a schematic diagram of the second magnetization direction of the second magnet in the vibration motor shown in Figure 1.
[0035] Figure 10 is a schematic diagram of the stator structure in the vibration motor shown in Figure 1.
[0036] Figure 11 is a schematic diagram of the moving part structure in the vibration motor of this application.
[0037] Figure 12 is an exploded view of the iron core unit in the moving part shown in Figure 11.
[0038] Figure 13 is an exploded view of the first structure of the housing in the vibration motor of this application.
[0039] Figure 14 is an exploded view of the second structure of the housing in the vibration motor of this application.
[0040] Wherein: 1-Stator (11-Outer shell (111-Receiving space, 112-Opening, 113-First surface, 114-Second surface, 115-Shell section (1151-First plate, 1152-Second plate), 116-Third plate, 117-Fourth plate), 12-Magnet assembly (121-First magnet (1211-First magnetization area, 1212-Second magnetization area), 122-Second magnet (1221-Third magnetization area, 1222-Fourth magnetization area)), 13-Pole core), 2 - Elastic element (21-through hole), 3-moving element (31-core unit (311-first core (3111-first core body, 3112-first protrusion, 3113-second protrusion), 312-second core (3121-first insertion hole), 313-third core (3131-second insertion hole)), 32-winding), a-first magnetic circuit, b-second magnetic circuit, c-third magnetic circuit, d-fourth magnetic circuit, e-fifth magnetic circuit, f-sixth magnetic circuit, g-seventh magnetic circuit, h-eighth magnetic circuit. Embodiments of the present invention
[0041] The present application will be further described below with reference to the accompanying drawings and embodiments.
[0042] This application provides a vibration motor, including a stator 1, an elastic element 2, and a mover 3 that vibrates along a first direction, as shown in Figures 1 to 6. The stator 1 includes a housing 11 and a magnet assembly 12. The housing 11 has a receiving space 111, and the magnet assembly 12 is received within the receiving space 111. The magnet assembly 12 includes two first magnets 121 and two second magnets 122. The two first magnets 121 are spaced apart and symmetrically fixed to the housing 11 in a second direction, and the two second magnets 122 are spaced apart and symmetrically fixed to the housing 11 in a third direction. The first direction, the second direction, and the third direction are perpendicular to each other. The mover 3 is suspended in the receiving space 111 at both ends of the first direction by the elastic element 2. The mover 3 includes an iron core unit 31 and a winding 32. The iron core unit 31 includes a first iron core 311, a second iron core 312, and a third iron core 313. The second iron core 312 and the third iron core 313 are symmetrically fixed to the two ends of the first iron core 311 in the first direction. The winding 32 is wound around the first iron core 311, and the winding 32 is located between the second iron core 312 and the third iron core 313.
[0043] The vibration motor of this embodiment includes a mover 3, a stator 1, and an elastic element 2 that vibrates along a first direction. The stator 1 includes a housing 11 with a receiving space 111 and a magnet assembly 12 housed within the receiving space 111. The magnet assembly 12 includes two first magnets 121 and two second magnets 122. The two first magnets 121 are spaced apart and symmetrically fixed to the housing 11 in a second direction, and the two second magnets 122 are spaced apart and symmetrically fixed to the housing 11 in a third direction. The mover 3 is suspended at both ends of the receiving space 11 by the elastic element 2 in the first direction. Within component 1, the mover 3 includes a core unit 31 and a winding 32. The core unit 31 includes a first core 311 and a second core 312 and a third core 313 symmetrically fixed at both ends of the first core 311 in a first direction. The winding 32 is wound around the first core 311 and located between the second core 312 and the third core 313. This design not only features a simple structure and low production cost but also facilitates assembly, further reducing production requirements and costs. In addition, the vibration motor in this embodiment is small in size and has high space utilization, providing a more powerful vibration experience within a smaller volume. When a periodic current is applied to the winding 32, the mover 3 experiences a periodic electromagnetic resultant force. This resultant force acts as an excitation source, driving the direct-drive vibration system composed of the mover 3, stator 1, and elastic element 2 to vibrate. This results in a fast response and a more realistic vibration sensation.
[0044] The vibration motor of this application embodiment has a simple structure and low cost. The appearance of the vibration motor can be made into a long strip shape as shown in Figure 1 or other shapes. The vibration motor of this application embodiment has strong performance and can provide a great vibration in a small volume. It can be applied to automotive steering wheels, central control systems, laptops, or other related fields.
[0045] As an example, the first direction can be the Z-axis, and the vibration motor in this embodiment can be a Z-axis linear motor.
[0046] In some preferred embodiments, referring to Figure 3, the winding 32 is arranged around a first direction. Referring to Figure 5, two first magnets 121 are magnetized along a second direction, and the magnetization directions of the two first magnets 121 are opposite. Referring to Figure 7, each first magnet 121 includes a first magnetized region 1211 and two second magnetized regions 1212. The two second magnetized regions 1212 are symmetrically arranged at both ends of the first magnetized region 1211 in the first direction, and the magnetization direction of the second magnetized regions 1212 is opposite to that of the first magnetized region 1211. Specifically, the first magnetized regions 1211 of the two first magnets 121 are correspondingly arranged, and the magnetization directions of the two first magnetized regions 1211 are opposite. The second magnetized regions 1212 of the two first magnets 121 are correspondingly arranged one-to-one, and the magnetization directions of the corresponding second magnetized regions 1212 are opposite. Please refer to Figure 8. The two second magnets 122 are magnetized in the third direction, and the magnetization directions of the two second magnets 122 are opposite.
[0047] In this embodiment, the excitation principle and magnetic circuit of the winding 32 and the magnet assembly 12 are shown in Figures 4 to 6. Under the excitation in the directions shown in Figures 4 to 6, the vibration system can form at least a first magnetic circuit a, a second magnetic circuit b, a third magnetic circuit c, a fourth magnetic circuit d, a fifth magnetic circuit e, a sixth magnetic circuit f, a seventh magnetic circuit g, and an eighth magnetic circuit h. Under the excitation in the directions shown in Figures 4 to 6, the mover 3 is subjected to electromagnetic force and Ampere force, with the resultant force F pointing downwards. It can be understood that when a current opposite to the direction shown in Figures 5 and 6 is applied to the winding 32, the resultant force on the mover 3 is upwards. When a periodic current is applied to the winding 32, the stator 1 will generate a periodic electromagnetic resultant force on the mover 3. This resultant force acts as an excitation source to drive the vibration system composed of the stator 1, the mover 3, and the spring sheet to vibrate.
[0048] In other preferred embodiments, referring to FIG9, the magnetization direction of the second magnet 122 is different from that shown in FIG6 and FIG8. Specifically, the second magnet 122 includes a third magnetization region 1221 and two fourth magnetization regions 1222. The two fourth magnetization regions 1222 are symmetrically arranged at both ends of the third magnetization region 1221 in the first direction, and the magnetization direction of the fourth magnetization regions 1222 is opposite to that of the third magnetization region 1221. Specifically, the third magnetization regions 1221 of the two second magnets 122 are correspondingly arranged, and the magnetization directions of the two third magnetization regions 1221 are opposite. The fourth magnetization regions 1222 of the two second magnets 122 are correspondingly arranged one-to-one, and the magnetization directions of the corresponding fourth magnetization regions 1222 are opposite. This embodiment is basically the same as the embodiments shown in FIG4 to FIG8, so the same parts will not be described again here.
[0049] In some embodiments, the first magnet 121 can be magnetized as a single unit. In other embodiments, the first magnet 121 can be magnetized separately.
[0050] In some embodiments, the second magnet 122 can be magnetized as a single unit. In other embodiments, the second magnet 122 can be magnetized separately.
[0051] In some preferred embodiments, referring to Figures 5 and 6, the outer casing 11 is a hollow structure and has two openings 112, which are arranged opposite to each other in a first direction. The hollow portion of the outer casing 11 is configured as a receiving space 111. The vibration motor includes two elastic elements 2, one of which is corresponding to one of the openings 112, and the other is corresponding to the other opening 112. The two ends of each elastic element 2 are fixed to the outer casing 11, so that each elastic element 2 spans across the corresponding opening 112, thereby reliably and effectively suspending the mover 3 within the receiving space 111.
[0052] In some preferred embodiments, referring to FIG4, the length of the housing 11 in the second direction is less than the length of the housing 11 in the third direction. The housing 11 includes two first surfaces 113 and two second surfaces 114. The two first surfaces 113 are spaced apart in the second direction, and the two second surfaces 114 are spaced apart in the third direction, together forming a receiving space 111. One first magnet 121 is fixed to one of the first surfaces 113, and the other first magnet 121 is fixed to the other first surface 113. One second magnet 122 is spaced apart from one of the second surfaces 114, and the other second magnet 122 is spaced apart from the other second surface 114. The elastic member 2 is fixed to the housing 11 at both ends in the third direction, thereby effectively improving the vibration.
[0053] In some preferred embodiments, referring to Figures 2, 3, 6, and 10, the stator 1 further includes two pole cores 13 housed within a housing space 111. Each pole core 13 is fixedly connected to a second magnet 122 in a one-to-one correspondence. The two second magnets 122 are disposed between the two pole cores 13, which can reduce magnetic leakage and achieve a high-efficiency magnetic field. The two pole cores 13 are spaced apart in a third direction and symmetrically fixed to the outer casing 11, with a gap between the pole cores 13 and the second surface 114.
[0054] Specifically, the pole core 13 can be set parallel to the second surface 114. The second magnet 122 can be fixed to the corresponding pole core 13 first, and then the pole core 13 can be fixed to the outer shell 11.
[0055] In some implementations, the pole core 13 may be made of a highly magnetic material.
[0056] In some embodiments, the housing 11 may be made of a strongly magnetic material.
[0057] In some embodiments, referring to Figure 3, the housing 11 can be a one-piece structure, which further reduces the assembly process of the vibration motor and makes it easier to assemble.
[0058] In some embodiments, referring to FIG13, for ease of processing, the outer shell 11 can be a split structure, formed by assembling two shell portions 115. The two shell portions 115 are centrally symmetrical about the central axis of the outer shell 11. Each shell portion 115 includes a first plate 1151 and a second plate 1152 formed by bending one end of the first plate 1151. The end of the first plate 1151 of one shell portion 115 away from the second plate 1152 is fixed to the second plate 1152 of the other shell portion 115, and the end of the second plate 1152 of the other shell portion 115 is fixed to the first plate 1151 of the other shell portion 115, thereby enclosing and forming a receiving space 111.
[0059] As an example, the two shell parts 115 can be fixedly connected by welding or other means.
[0060] In some embodiments, referring to FIG14, to further simplify the structure of the outer casing 11, the outer casing 11 may be assembled from two third plates 116 and two fourth plates 117. The two third plates 116 are spaced apart and symmetrically arranged, and the two fourth plates 117 are spaced apart and symmetrically arranged. The two third plates 116 are connected by the two fourth plates 117 to enclose and form a receiving space 111.
[0061] As an example, the third plate 116 and the fourth plate 117 can be fixedly connected by welding or other means.
[0062] In some preferred embodiments, referring to FIG3, the elastic element 2 can be a spring sheet, and the elastic element 2 has a through hole 21. The first iron core 311 includes a first iron core body 3111, a first protrusion 3112 and a second protrusion 3113. The first protrusion 3112 extends from the first iron core body 3111 along a first direction toward the second iron core 312 and is connected to the second iron core 312. The second protrusion 3113 extends from the first iron core body 3111 along the first direction toward the third iron core 313 and is connected to the third iron core 313. The first protrusion 3112 and the second protrusion 3113 are symmetrically arranged in the first direction, and the first protrusion 3112 is inserted and fixed in the through hole 21 of one of the elastic elements 2, and the second protrusion 3113 is inserted and fixed in the through hole 21 of the other elastic element 2.
[0063] In some embodiments, referring to Figures 3 and 12, the first protrusion 3112 can be a stepped structure. It should be noted that in other embodiments, the first protrusion 3112 can be a structure of other shapes. For example, the first protrusion 3112 can be a cylinder, a square, or any other arbitrary protruding shape, which can be set according to the actual situation, and will not be elaborated here.
[0064] In some embodiments, referring to Figures 3 and 12, the second protrusion 3113 can be a stepped structure. It should be noted that in other embodiments, the second protrusion 3113 can be a structure of other shapes. For example, the second protrusion 3113 can be a cylinder, a square, or any other arbitrary protruding shape, which can be set according to the actual situation, and will not be elaborated here.
[0065] In some embodiments, the core unit 31 may be made of a highly magnetically permeable material. For example, the first core 311 may be made of a highly magnetically permeable material, the second core 312 may be made of a highly magnetically permeable material, and the third core 313 may be made of a highly magnetically permeable material.
[0066] In some embodiments, the core unit 31 can be an integrally formed structure, that is, the first core 311, the second core 312 and the third core 313 are an integral structure, which further reduces the assembly process of the vibration motor and makes it easier to assemble.
[0067] In some embodiments, referring to Figure 3, the core unit 31 can be a split structure. A second core 312 is mounted at one end of the first core 311 in a first direction. Specifically, the second core 312 is mounted at the end of the first core 311 having a first protrusion 3112, and the second core 312 has a first insertion hole 3121 that engages with the first protrusion 3112. A third core 313 is mounted at the other end of the first core 311 in the first direction. Specifically, the third core 313 is mounted at the end of the first core 311 having a second protrusion 3113, and the third core 313 has a second insertion hole 3131 that engages with the second protrusion 3113.
[0068] In some embodiments, referring to Figures 11 and 12, the core unit 31 can be a partially split structure. The first core 311 and the second core 312 are an integral structure, and the third core 313 is mounted on the first core 311. The third core 313 has a second insertion hole 3131 that engages with the second protrusion 3113.
[0069] In some embodiments, the first iron core 311 can be formed by stacking multiple layers of iron sheets, thereby reducing eddy current losses. It should be noted that in other embodiments, the first iron core 311 can also be a one-piece structure, which can be set according to the actual situation, and will not be elaborated here.
[0070] In some embodiments, the second iron core 312 can be formed by stacking multiple layers of iron sheets, thereby reducing eddy current losses. It should be noted that in other embodiments, the second iron core 312 can also be a one-piece structure, which can be set according to the actual situation, and will not be elaborated here.
[0071] In some embodiments, the third core 313 can be formed by stacking multiple layers of iron sheets, thereby reducing eddy current losses. It should be noted that in other embodiments, the third core 313 can also be a one-piece structure, which can be set according to the actual situation, and will not be elaborated here.
[0072] The above description is merely an embodiment of this application. It should be noted that those skilled in the art can make improvements without departing from the inventive concept of this application, but these improvements all fall within the protection scope of this application.
Claims
1. A vibration motor, characterized in that, include: Stator, elastic element, and mover vibrating in the first direction; The stator includes a housing with a receiving space and a magnet assembly housed within the receiving space. The magnet assembly includes two first magnets and two second magnets. The two first magnets are spaced apart and symmetrically fixed to the housing in a second direction, and the two second magnets are spaced apart and symmetrically fixed to the housing in a third direction. The first direction, the second direction, and the third direction are perpendicular to each other. The mover is suspended in the receiving space at both ends of the first direction by the elastic element. The mover includes an iron core unit and a winding. The iron core unit includes a first iron core and a second iron core and a third iron core symmetrically fixed at both ends of the first iron core in the first direction. The winding is wound around the first iron core and located between the second iron core and the third iron core.
2. The vibration motor as described in claim 1, characterized in that, The winding is arranged around the first direction; The two first magnets are respectively magnetized along the second direction and their magnetization directions are opposite. The first magnet includes a first magnetized region and a second magnetized region symmetrically disposed at both ends of the first magnetized region in the first direction. The magnetization direction of the second magnetized region is opposite to that of the first magnetized region. The two second magnets are magnetized along the third direction respectively, and their magnetization directions are opposite.
3. The vibration motor as described in claim 2, characterized in that, The second magnet includes a third magnetized region and a fourth magnetized region symmetrically disposed at both ends of the third magnetized region in the first direction, wherein the magnetization direction of the fourth magnetized region is opposite to that of the third magnetized region.
4. The vibration motor as described in claim 1, characterized in that, The outer shell is a hollow structure with two openings, which are arranged opposite to each other in the first direction, and the hollow portion of the outer shell is configured as the receiving space; The vibration motor includes two elastic elements, each corresponding to one of the openings. The two ends of the elastic elements are fixed to the outer shell, so that each elastic element spans across the corresponding opening.
5. The vibration motor as described in claim 4, characterized in that, The length of the housing in the second direction is less than the length of the housing in the third direction. The housing includes two first surfaces spaced apart in the second direction and two second surfaces spaced apart in the third direction. The two first surfaces and the two second surfaces enclose the receiving space. The first magnet is fixed to the first surface; There is a gap between the second magnet and the second surface; The elastic element is fixed to the outer shell at both ends in the third direction.
6. The vibration motor as described in claim 5, characterized in that, The stator further includes two pole cores housed within the housing space. The two pole cores are spaced apart in the third direction and symmetrically fixed to the outer shell, and there is a gap between the pole cores and the second surface. Two second magnets are disposed between the two pole cores and are respectively fixed to the corresponding pole cores.
7. The vibration motor as described in claim 1, characterized in that, The elastic element has a through hole; The first iron core includes a first iron core body, a first protrusion extending from the first iron core body along the first direction toward the second iron core and connecting to the second iron core, and a second protrusion extending from the first iron core body along the first direction toward the third iron core and connecting to the third iron core. The first protrusion and the second protrusion are symmetrically arranged in the first direction, and the first protrusion and the second protrusion are respectively inserted into the through hole of the corresponding elastic member.
8. The vibration motor as described in claim 7, characterized in that, The second iron core has a first insertion hole that engages with the first protrusion, and the third iron core has a second insertion hole that engages with the second protrusion.
9. The vibration motor as described in claim 1, characterized in that, At least one of the first iron core, the second iron core, and the third iron core is formed by stacking multiple layers of iron sheets.