Patent Publication Number: US-2023164253-A1

Title: Folding Apparatus and Electronic Device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/CN2021/087451, filed on Apr. 15, 2021, which claims priority to Chinese Patent Application No. 202010295201.4, filed on Apr. 15, 2020. Both of the aforementioned applications are hereby incorporated by reference in their entireties. 
     TECHNICAL FIELD 
     This application relates to the field of foldable electronic product technologies, and in particular, to a folding apparatus and an electronic device. 
     BACKGROUND 
     In recent years, flexible displays are widely applied to various foldable electronic devices because of advantages such as lightness, thinness, and non-fragility. The foldable electronic device further includes a folding apparatus configured to bear the flexible display. The folding apparatus usually includes two housings and a rotating mechanism connected between the two housings. The two housings are folded or unfolded relative to each other through deformation of the rotating mechanism, to drive folding or unfolding of the flexible display. However, when a conventional folding apparatus is folded or unfolded, because a length of a bearing surface of the conventional folding apparatus that is used to bear a flexible display is changed significantly, the flexible display tends to be stretched in a folding process and squeezed in an unfolding process. As a result, the flexible display is easily damaged, and a service life of the flexible display is shortened. 
     SUMMARY 
     An objective of this application is to provide a folding apparatus and an electronic device. The folding apparatus is configured to bear a flexible display. According to this application, when the folding apparatus is folded or unfolded, a risk that the flexible display is stretched or squeezed is low, so that reliability of the flexible display is high, and a service life of the flexible display is long. 
     According to a first aspect, this application provides a folding apparatus. The folding apparatus may be applied to a foldable electronic device, and is configured to bear a flexible display. The folding apparatus includes a first housing, a rotating mechanism, and a second housing that are connected sequentially. The rotating mechanism can deform, so that the first housing and the second housing are folded or unfolded relative to each other. 
     The rotating mechanism includes a main shaft assembly, a first fixed bracket, a first transmission arm, a first rotating arm, a second fixed bracket, a second transmission arm, and a second rotating arm. The first fixed bracket is fastened to the first housing, the first transmission arm includes a sliding end and a rotating end, the sliding end of the first transmission arm is slidably connected to the first fixed bracket, the rotating end of the first transmission arm is rotatably connected to the main shaft assembly, one end of the first rotating arm is rotatably connected to the first fixed bracket, and the other end of the first rotating arm is rotatably connected to the main shaft assembly. The second fixed bracket is fastened to the second housing, the second transmission arm includes a sliding end and a rotating end, the sliding end of the second transmission arm is slidably connected to the second fixed bracket, the rotating end of the second transmission arm is rotatably connected to the main shaft assembly, one end of the second rotating arm is rotatably connected to the second fixed bracket, and the other end of the second rotating arm is rotatably connected to the main shaft assembly. 
     In this application, the rotating mechanism controls motion tracks of the first fixed bracket and the first housing by using both the first transmission arm and the first rotating arm, and controls motion tracks of the second fixed bracket and the second housing by using both the second transmission arm and the second rotating arm. Therefore, when the first housing and the second housing are folded relative to each other, the rotating mechanism enables the first fixed bracket to drive the first housing to approach the main shaft assembly, and enables the second fixed bracket to drive the second housing to approach the main shaft assembly. When the first housing and the second housing are unfolded relative to each other, the rotating mechanism enables the first fixed bracket drive the first housing to move away from the main shaft assembly, and enables the second fixed bracket to drive the second housing to move away from the main shaft assembly. In other words, the rotating mechanism can implement pulling-in of the housing when the folding apparatus is switched from a flattened state to a closed state and pushing-out of the housing when the folding apparatus is switched from the closed state to the flattened state, so that the folding apparatus can implement deformation by using the flexible display as a neutral surface when being unfolded or folded. In this way, a risk that the flexible display is stretched or squeezed is reduced, to protect the flexible display and improve reliability of the flexible display, so that the flexible display and the electronic device have long service lives. 
     When the first housing and the second housing are folded relative to each other to the closed state by using the rotating mechanism, the first housing and the second housing can be completely closed, and there is no gap between the first housing and the second housing or a gap between the first housing and the second housing is small. Therefore, appearance integrity of the folding apparatus is implemented, and self-shielding in appearance is implemented. Appearance integrity of the electronic device to which the folding apparatus is applied is implemented, so that product reliability and user experience are improved. 
     In addition, the first transmission arm is rotatably connected to the main shaft assembly and slidably connected to the first fixed bracket to form a link-slider structure, and the first rotating arm is rotatably connected to the main shaft assembly and rotatably connected to the first fixed bracket to form a link structure. The second transmission arm is rotatably connected to the main shaft assembly and is slidably connected to the second fixed bracket to form a link-slider structure. The second rotating arm is rotatably connected to the main shaft assembly and rotatably connected to the second fixed bracket to form a link structure. In the rotating mechanism, the housing is connected to the main shaft assembly by using the link-slider structure and the link structure. A quantity of components of the rotating mechanism is small, a cooperation relationship and a cooperation position are simple, and the components are easy to manufacture and assemble. This facilitates mass production. In addition, because the main shaft assembly is associated with the first fixed bracket by using the first transmission arm and the first rotating arm, and the main shaft assembly is associated with the second fixed bracket by using the second transmission arm and the second rotating arm, the rotating mechanism has a better mechanism stretching-resistance capability and mechanism squeezing-resistance capability. 
     In a possible implementation, the main shaft assembly includes a main inner shaft and a main outer shaft that is fastened to the main inner shaft, and when the first housing and the second housing are folded relative to each other to a closed state, the main inner shaft is located between the main outer shaft and each of the first fixed bracket and the second fixed bracket. 
     A rotation center around which the first transmission arm rotates relative to the main shaft assembly is close to the main inner shaft and away from the main outer shaft, and a rotation center around which the first rotating arm rotates relative to the main shaft assembly is close to the main outer shaft and away from the main inner shaft. A rotation center around which the second transmission arm rotates relative to the main shaft assembly is close to the main inner shaft and away from the main outer shaft, and a rotation center around which the second rotating arm rotates relative to the main shaft assembly is close to the main outer shaft and away from the main inner shaft. 
     In this implementation, locations of the rotation center around which the first transmission arm rotates relative to the main shaft assembly, the rotation center around which the first rotating arm rotates relative to the main shaft assembly, the rotation center around which the second transmission arm rotates relative to the main shaft assembly, and the rotation center around which the second rotating arm rotates relative to the main shaft assembly are set, so that the rotating mechanism can more easily implement pulling-in of the housing when the folding apparatus is switched from the flattened state to the closed state and pushing-out of the housing when the folding apparatus is switched from the closed state to the flattened state. 
     In a possible implementation, a plurality of three-dimensional space structures are disposed on both the main inner shaft and the main outer shaft. These structures are designed, so that after the main inner shaft and the main outer shaft are assembled, the main inner shaft and the main outer shaft can jointly form a plurality of movement spaces, and mechanical parts of the rotating mechanism are movably disposed in the plurality of movement spaces of the main shaft assembly, to implement connection to the main shaft assembly. A split design of the main inner shaft and the main outer shaft helps reduce manufacturing difficulty of the main shaft assembly, and improve manufacturing precision and a product yield of the main shaft assembly. 
     In a possible implementation, the main inner shaft and the main outer shaft of the main shaft assembly jointly enclose a plurality of arc-shaped grooves. The rotating end of the first transmission arm is arc-shaped and is disposed in one of the arc-shaped grooves, and an end that is of the first rotating arm and that is rotatably connected to the main shaft assembly is arc-shaped and is disposed in another arc-shaped groove. The rotating end of the second transmission arm is arc-shaped and is disposed in another arc-shaped groove, and an end that is of the second rotating arm and that is rotatably connected to the main shaft assembly is arc-shaped and is disposed in another arc-shaped groove. 
     In this implementation, the first transmission arm is connected to the main shaft assembly by using a virtual shaft, the first rotating arm is connected to the main shaft assembly by using a virtual shaft, the second transmission arm is connected to the main shaft assembly by using a virtual shaft, and the second rotating arm is connected to the main shaft assembly by using a virtual shaft. A rotatable connection has a simple structure and occupies small space. This helps reduce a thickness of the rotating mechanism, so that the folding apparatus and the electronic device are more light and thin. 
     In a possible implementation, there is a first arc-shaped groove on the first fixed bracket, and an end that is of the first rotating arm and that is rotatably connected to the first fixed bracket is arc-shaped and is disposed in the first arc-shaped groove. There is a second arc-shaped groove on the second fixed bracket, and an end that is of the second rotating arm and that is rotatably connected to the second fixed bracket is arc-shaped and is disposed in the second arc-shaped groove. 
     In this implementation, the first rotating arm is connected to first fixed bracket by using a virtual shaft, and the second rotating arm is connected to the second fixed bracket by using a virtual shaft. In this way, a rotatable connection has a simple structure and occupies small space. This helps reduce a thickness of the rotating mechanism, so that the folding apparatus and the electronic device are more light and thin. 
     In a possible implementation, the first fixed bracket includes a first fixed base and a first fastener, and the first fastener is fastened to the first fixed base, and encloses the first arc-shaped groove with the first fixed base. In this implementation, a processing manner is used in which the first fixed base and the first fastener are separately manufactured, and then the first fixed base and the first fastener are assembled into the first fixed bracket. This helps reduce processing difficulty of the first fixed bracket, and improve a product yield of the first fixed bracket. The first fastener and the first fixed base may be fastened to each other by using a fastener. 
     In a possible implementation, the first fastener has an arc surface used to enclose the first arc-shaped groove, and a limiting groove is formed on a middle part of the arc surface and configured to limit, in an axial direction of the main shaft assembly, the first rotating arm disposed in the first arc-shaped groove, to improve reliability of a connection structure. In some other implementations, the limiting groove may alternatively be formed on an arc surface that is of the first fixed base and that is used to enclose the first arc-shaped groove. The first fastener may further have a stop block, configured to prevent the first rotating arm disposed in the first arc-shaped groove from being accidentally detached from the first arc-shaped groove. 
     In a possible implementation, the second fixed bracket includes a second fixed base and a second fastener. The second fastener is fastened to the second fixed base, and encloses a second arc-shaped groove with the second fixed base. 
     In a possible implementation, an end that is of the first rotating arm and that is connected to the first fixed bracket includes a limiting bulge and a limiting projection. The limiting bulge is configured to cooperate with the limiting groove of the first arc-shaped groove. The limiting projection is configured to cooperate with the stop block of the first fixed bracket. In a possible implementation, an end that is of the first rotating arm and that is connected to the main shaft assembly includes a limiting bulge and a limiting projection. The limiting bulge is configured to cooperate with a limiting groove of the main shaft assembly. The limiting projection is configured to cooperate with a limiting projection of the main shaft assembly. 
     In this implementation, the first rotating arm is approximately in a “W” shape. The first rotating arm is connected to the first fixed bracket by using a virtual shaft, and the first rotating arm is also connected to the main shaft assembly by using a virtual shaft. In this way, a rotatable connection has a simple structure and occupies small space. This helps reduce a thickness of the rotating mechanism, so that the folding apparatus and the electronic device are more light and thin. 
     In a possible implementation, there is a first sliding slot and a first accommodating slot on the first fixed bracket, and the first accommodating slot communicates with the first sliding slot. The rotating mechanism further includes a first limiting component, the first limiting component is disposed in the first accommodating slot. The sliding end of the first transmission arm is disposed in the first sliding slot, there is a first recessed area and a second recessed area on the sliding end of the first transmission arm, and the second recessed area is located between the first recessed area and the rotating end of the first transmission arm. When the first housing and the second housing are unfolded relative to each other to the flattened state, the first limiting component is partially clamped into the first recessed area. When the first housing and the second housing are folded relative to each other to the closed state, the first limiting component is partially clamped into the second recessed area. 
     In this implementation, the first limiting component is clamped to the sliding end of the first transmission arm to limit the first transmission arm, so that the first transmission arm and the first fixed bracket can maintain a preset relative position relationship when no large external force is applied, the rotating mechanism can stay at a preset angle, and the rotating mechanism can maintain the flattened state or the closed state. In this way, user experience of the folding apparatus and the electronic device is improved. 
     In a possible implementation, there is a recessed guiding space on a side wall of the first sliding slot, the sliding end of the first transmission arm includes a first flange on a circumferential side, the first flange is disposed in the guiding space of the first sliding slot, and the first recessed area and the second recessed area are formed on the first flange. The guiding space of the first sliding slot cooperates with the first flange of the first transmission arm, so that the sliding end of the first transmission arm can be guided in a sliding direction of the first sliding slot. In this way, a relative sliding action between the first transmission arm and the first fixed bracket is easier to implement and control precision is higher. 
     In a possible implementation, the first limiting component includes a first bracket and a first elastic part. The first bracket is a rigid structure and is not easy to deform under an external force. The first elastic part is an elastic structure and is easy to deform under an external force. The first bracket includes a control part and an abutting part, one end of the first elastic part is disposed on the control part of the first bracket, the other end of the first elastic part abuts against a slot wall of the first accommodating slot, and the abutting part of the first bracket is clamped to the sliding end of the first transmission arm. 
     In this implementation, because the first elastic part of the first limiting component can deform under an external force, the first limiting component can smoothly move between the first recessed area and the second recessed area relative to the sliding end of the first transmission arm, to improve reliability of limiting between the first limiting component and the sliding end of the first transmission arm. 
     In a possible implementation, the first limiting component may further include a first elastic part, and the first elastic part is disposed on the abutting part of the first bracket. The first elastic part may be made of a material (for example, rubber) with low rigidity, so that when subject to an external force, the first elastic part can absorb an impact force through deformation, to implement cushioning. Because the first elastic part is sleeved on the abutting part of the first bracket, the first limiting component abuts against the sliding end of the first transmission arm by using the first elastic part having a cushioning function. This helps reduce a risk of wearing the first bracket and the first transmission arm in a long-time relative movement, improve limiting reliability of the first limiting component, and improve reliability of the rotating assembly. 
     In a possible implementation, the first bracket of the first limiting component may further include a positioning part. The positioning part is fastened below the abutting part, and protrudes relative to the abutting part in a direction away from the control part. Two adjacent surfaces of the first flange of the first transmission arm respectively abut the abutting part of the first bracket and the positioning part of the first bracket, so that the first flange can slide relative to the positioning part of the first bracket. The positioning part of the first bracket is disposed, so that a limiting connection relationship between the first limiting component and the sliding end of the first transmission arm is more reliable, to improve reliability of the rotating assembly. 
     In a possible implementation, the rotating mechanism further includes a first synchronous swing arm and a second synchronous swing arm. The first synchronous swing arm includes a rotating end and a movable end, the rotating end of the first synchronous swing arm is rotatably connected to the main shaft assembly, the movable end of the first synchronous swing arm is movably connected to the first fixed bracket, and when the first housing and the second housing are folded or unfolded relative to each other, the movable end of the first synchronous swing arm slides and rotates relative to the first fixed bracket. The second synchronous swing arm includes a rotating end and a movable end, the rotating end of the second synchronous swing arm is rotatably connected to the main shaft assembly, the rotating end of the second synchronous swing arm is engaged with the rotating end of the first synchronous swing arm, the movable end of the second synchronous swing arm is movably connected to the second fixed bracket, and when the first housing and the second housing are folded or unfolded relative to each other, the movable end of the second synchronous swing arm slides and rotates relative to the second fixed bracket. 
     In this implementation, the rotating end of the first synchronous swing arm and the rotating end of the second synchronous swing arm are engaged with each other, and both the rotating end of the first synchronous swing arm and the rotating end of the second synchronous swing arm are rotatably connected to the main shaft assembly, the movable end of the first synchronous swing arm is movably connected to the first fixed bracket, and the movable end of the second synchronous swing arm is movably connected to the second fixed bracket. Therefore, when the first housing and the second housing are unfolded or folded relative to each other, the first synchronous swing arm and the second synchronous swing arm can control rotation angles of the first fixed bracket and the second fixed bracket to be consistent relative to the main shaft assembly, so that rotation actions of the first housing and the second housing are synchronous and consistent. Symmetry of folding actions and unfolding actions of the folding apparatus is high. This helps improve user experience. 
     The first synchronous swing arm is rotatably connected to the main shaft assembly, and slidably and rotatably connected to the first fixed bracket, so that a link-slider structure is formed. The second synchronous swing arm is rotatably connected to the main shaft assembly, and slidably and rotatably connected to the second fixed bracket, so that a link-slider structure is formed. The two link-slider structures that are engaged with each other can effectively control the rotation actions of the first housing and the second housing to be synchronous and consistent. 
     In a possible implementation, the rotating end of the first synchronous swing arm includes a first rotating body, a first rotating shaft, and a first gear, the first rotating shaft is fastened to a front facet and/or a back facet of the first rotating body, the first gear is fastened to a circumferential side facet of the first rotating body, and the first rotating shaft is rotatably connected to the main shaft assembly. 
     The rotating end of the second synchronous swing arm includes a second rotating body, a second rotating shaft, and a second gear, the second rotating shaft is fastened to a front facet and/or a back facet of the second rotating body, the second gear is fastened to a circumferential side facet of the second rotating body, the second rotating shaft is rotatably connected to the main shaft assembly, and the second gear is engaged with the first gear. 
     In this implementation, the rotating end of the first synchronous swing arm and the rotating end of the second synchronous swing arm are directly engaged with each other by using the first gear and the second gear, so that a synchronization assembly jointly formed by the first synchronous swing arm and the second synchronous swing arm has a simple structure, a movement process is easy to control, and accuracy is high. 
     In a possible implementation, there is a third sliding slot on the first fixed bracket, there is a recessed guiding space on a slot wall of the third sliding slot, the movable end of the first synchronous swing arm has a third rotating shaft, the first synchronous swing arm is disposed in the third sliding slot, and the third rotating shaft is disposed in the guiding space of the third sliding slot. There is a fourth sliding slot on the second fixed bracket, there is a recessed guiding space on a slot wall of the fourth sliding slot, the movable end of the second synchronous swing arm has a fourth rotating shaft, the second synchronous swing arm is disposed in the fourth sliding slot, and the fourth rotating shaft is disposed in the guiding space of the fourth sliding slot. 
     In this implementation, the guiding space of the third sliding slot cooperates with the first rotating shaft of the first synchronous swing arm, so that the movable end of the first synchronous swing arm can be guided in a sliding direction of the third sliding slot. In this way, a relative movement action between the first synchronous swing arm and the first fixed bracket is easier to implement and control precision is higher. The guiding space of the fourth sliding slot cooperates with the fourth rotating shaft of the second synchronous swing arm, so that the movable end of the second synchronous swing arm can be guided in a sliding direction of the fourth sliding slot. In this way, a relative movement action between the second synchronous swing arm and the second fixed bracket is easier to implement and control precision is higher. 
     In some other implementations, the first synchronous swing arm may alternatively be connected to the first fixed bracket by using a connector, and the second synchronous swing arm may alternatively be connected to the second fixed bracket by using a connector. For example, the rotating mechanism further includes a first connector and a second connector. The first connector is slidably disposed in the guiding space of the third sliding slot, the first rotating shaft is rotatably connected to the first connector, the second connector is slidably disposed in the guiding space of the fourth sliding slot, and the second rotating shaft is rotatably connected to the second connector. 
     In a possible implementation, the rotating mechanism further includes a first supporting plate and a second supporting plate, the first supporting plate is fixedly connected to the sliding end of the first transmission arm, and the second supporting plate is fixedly connected to the sliding end of the second transmission arm. When the first housing and the second housing are unfolded relative to each other to the flattened state, the first supporting plate is flush with the second supporting plate, the first supporting plate is laid between the first fixed bracket and the main shaft assembly, and the second supporting plate is laid between the second fixed bracket and the main shaft assembly. When the first housing and the second housing are folded relative to each other to the closed state, the first supporting plate is stacked on a side that is of the first fixed bracket and that is away from the second fixed bracket, and the second supporting plate is stacked on a side that is of the second fixed bracket and that is away from the first fixed bracket. 
     In this implementation, when the first housing and the second housing are unfolded relative to each other to the flattened state, the first supporting plate, the main shaft assembly, and the second supporting plate can jointly form a complete planar support for a bending part of the flexible display. When the first housing and second housing are folded relative to each other to the closed state, the first supporting plate and the second supporting plate can slide and be accommodated relative to the first housing and the second housing respectively, so that the main shaft assembly is exposed to form complete support for the bending part of the flexible display. In other words, when the folding apparatus is in the flattened state or the closed state, the rotating mechanism can completely support the bending part of the flexible display, thereby helping protect the flexible display and improving user experience. 
     In a possible implementation, the main shaft assembly has a supporting surface. When the first housing and the second housing are folded relative to each other to the closed state, the supporting surface of the main shaft assembly is exposed relative to the first supporting plate and the second supporting plate. The supporting surface of the main shaft assembly is arc-shaped. 
     In this implementation, when the first housing and the second housing are folded relative to each other to a closed state, the main shaft assembly can provide a complete-semicircle or nearly-semicircle support for the bending part of the flexible display, which is consistent with an ideal closed form of the bending part of the flexible display, so that more optimized support can be provided for the flexible display in the closed form. 
     In a possible implementation, the rotating mechanism further includes a first shielding plate and a second shielding plate. The first shielding plate is fixedly connected to the sliding end of the first transmission arm, and the second shielding plate is fixedly connected to the sliding end of the second transmission arm. The first shielding plate is located on a side that is of the first transmission arm and that faces away from the first supporting plate, and the second shielding plate is located on a side that is of the second transmission arm and that faces away from the second supporting plate. 
     When the first housing and the second housing are unfolded relative to each other to the flattened state, the first shielding plate is flush with the second shielding plate, the first shielding plate is laid between the first fixed bracket and the main shaft assembly, and the second shielding plate is laid between the second fixed bracket and the main shaft assembly. When the first housing and the second housing are folded relative to each other to the closed state, the first shielding plate is located between the first fixed bracket and the first housing, and the second shielding plate is located between the second fixed bracket and the second housing. 
     In this implementation, when the first housing and the second housing are unfolded relative to each other to the flattened state, the first shielding plate is flush with the second shielding plate, the first shielding plate is laid between the first fixed bracket and the main shaft assembly, and can shield a gap between the first fixed bracket and the main shaft assembly, and the second shielding plate is laid between the second fixed bracket and the main shaft assembly, and can shield a gap between the second fixed bracket and the main shaft assembly. Therefore, the folding apparatus can implement self-shielding. In this way, appearance integrity is improved, a risk that dust, sundries, and the like enter the rotating mechanism from outside can also be lowered, to ensure reliability of the folding apparatus. When the first housing and the second housing are folded relative to each other to the closed state, the first shielding plate can be accommodated between the first fixed bracket and the first housing, and the second shielding plate can be accommodated between the second fixed bracket and the second housing, so that avoidance is achieved. In this way, the folding apparatus can be smoothly folded to the closed form, and mechanism reliability is high. 
     In this implementation, the first supporting plate and the first shielding plate are fastened to the sliding end of the first transmission arm, and the first supporting plate and the first shielding plate move with the sliding end of the first transmission arm, and the second supporting plate and the second shielding plate are fastened to the sliding end of the second transmission arm, and the second supporting plate and the second shielding plate move with the sliding end of the second transmission arm. Therefore, when the folding apparatus is switched from the closed state to the flattened state or when the folding apparatus is switched from the flattened state to the closed state, the first supporting plate and the second supporting plate gradually approach the main shaft assembly or move away from the main shaft assembly, so that the folding apparatus can completely support the flexible display in various forms. In this way, reliability of the flexible display and the electronic device is improved and service lives of the flexible display and the electronic device are increased. In addition, when the folding apparatus is switched from the closed state to the flattened state or when the folding apparatus is switched from the flattened state to the closed state, the first shielding plate and the second shielding plate gradually approach the main shaft assembly or move away from the main shaft assembly, so that the folding apparatus in the various forms can adapt to forms of the rotating mechanism, to implement self-shielding. In this way, mechanism reliability is high. 
     Moreover, because both the first supporting plate and the first shielding plate are fastened to the sliding end of the first transmission arm, and both the second supporting plate and the second shielding plate are fastened to the sliding end of the second transmission arm, the first transmission arm and the second transmission arm not only control rotation actions of the first housing and the second housing, but also control extending or retracting of the first supporting plate, the first shielding plate, the second supporting plate, and the second shielding plate. Therefore, the rotating mechanism is highly integrated, an overall connection relationship is simple, and mechanism reliability is high. 
     In a possible implementation, the main shaft assembly has a shielding surface. When the first housing and the second housing are unfolded relative to each other to the flattened state, the shielding surface of the main shaft assembly is exposed relative to the first shielding plate and the second shielding plate. Therefore, the first shielding plate, the main shaft assembly, and the second shielding plate can jointly shield a gap between the first housing and the second housing, so that the rotating mechanism can implement self-shielding in the flattened state. This improves appearance integrity. 
     In a possible implementation, the main shaft assembly further includes a shielding plate, and the shielding plate is fastened on a side that is of the main inner shaft and that faces away from the main outer shaft. The shielding surface of the main shaft assembly is formed on the shielding plate, and the shielding surface is disposed to face away from the main inner shaft. The shielding plate may be integrated with the main inner shaft, or the shielding plate and the main inner shaft may be fastened to each other in an assembled manner. 
     In a possible implementation, the rotating mechanism further includes a third transmission arm, a third fixed bracket, a fourth transmission arm, and a fourth fixed bracket, the third fixed bracket is fastened to the first housing, one end of the third transmission arm is rotatably connected to the main shaft assembly, the other end of the third transmission arm is slidably connected to the third fixed bracket, the fourth fixed bracket is fastened to the second housing, one end of the fourth transmission arm is rotatably connected to the main shaft assembly, and the other end of the fourth transmission arm is slidably connected to the fourth fixed bracket. 
     In this implementation, the third transmission arm, the third fixed bracket, the fourth transmission arm, and the fourth fixed bracket are disposed in the rotating mechanism to increase interaction force between the first housing and the second housing, and the rotating mechanism, so that the folding apparatus is easier to fold and unfold. 
     In a possible implementation, there is a fifth sliding slot on the third fixed bracket, and a middle part of a slot wall of the fifth sliding slot is recessed to form a guiding space of the fifth sliding slot. The third transmission arm includes a sliding end and a rotating end. The sliding end of the third transmission arm has a third flange. The sliding end of the third transmission arm is disposed in the fifth sliding slot, and the third flange is disposed in the guiding space of the fifth sliding slot. The rotating end of the third transmission arm is arc-shaped and is disposed in one of the arc-shaped grooves of the main shaft assembly. In this case, the third transmission arm is rotatably connected to the main shaft assembly by using a virtual shaft. 
     In a possible implementation, a rotation center around which the third transmission arm rotates relative to the main shaft assembly and the rotation center around which the first transmission arm rotates relative to the main shaft assembly are collinear. A rotation center around which the fourth transmission arm rotates relative to the main shaft assembly and the rotation center around which the second transmission arm rotates relative to the main shaft assembly are collinear. 
     In this implementation, the rotation centers around which the third transmission arm and the first transmission arm rotate relative to the main shaft assembly are collinear, and the third transmission arm is slidably connected to the third fixed bracket, and the rotation centers around which the fourth transmission arm and the second transmission arm rotate relative to the main shaft assembly are collinear, and the fourth transmission arm is slidably connected to the fourth fixed bracket. In this way, movement of the third transmission arm can be synchronized with movement of the first transmission arm, and movement of the fourth transmission arm can be synchronized with movement of the second transmission arm, so that a structure design and a connection relationship of the rotating mechanism can be simplified, and reliability of the rotating structure is improved. In addition, a structure of the third transmission arm may be the same as a structure of the first transmission arm, and a structure of the fourth transmission arm may be the same as a structure of the second transmission arm, to reduce design difficulty of the rotating mechanism. 
     In a possible implementation, there is a first fixed groove on a side that is of the first housing and that is close to the rotating mechanism, the first housing includes a first positioning plate located in the first fixed groove, the first positioning plate and a groove bottom wall of the first fixed groove are spaced, and the first fixed bracket is located between the first positioning plate and the groove bottom wall of the first fixed groove, and is fixedly connected to the first positioning plate. In this implementation, because the first fixed bracket and the first housing are fastened to each other, the first housing moves with the first fixed bracket, and the rotating mechanism may control a motion trail of the first housing by controlling a motion trail of the first fixed bracket. 
     In a possible implementation, the first housing has a first supporting surface, and the first positioning plate sinks relative to the first supporting surface to form a first accommodating groove. The first accommodating groove can provide an accommodation and movement space for the first supporting plate. A location at which the first accommodating groove is disposed enables a supporting surface of the first supporting plate disposed in the first accommodating groove to be flush with the first supporting surface of the first housing. In this way, the first supporting plate can better support the flexible display. A depth of the first accommodating groove is very shallow, and a supporting backplane with high hardness is disposed on a non-display side of the flexible display. Therefore, when the first supporting plate partially extends out of the first accommodating groove, a part that is of the flexible display and that faces the first accommodating groove does not deform significantly when been pressed by a user. This also ensures reliability of the flexible display. 
     In a possible implementation, the third fixed bracket is located between the first positioning plate and the groove bottom wall of the first fixed groove, and is fixedly connected to the first positioning plate. A gap is formed between the two first fixed brackets and the third fixed bracket, and the groove bottom wall of the first fixed groove, and the gap is used to provide an accommodation and movement space for the first shielding plate. 
     In a possible implementation, there is a second fixed groove on a side that is of the second housing and that is close to the rotating mechanism, the second housing includes a second positioning plate located in the second fixed groove, the second positioning plate and a groove bottom wall of the second fixed groove are spaced, and the second fixed bracket is located between the second positioning plate and the groove bottom wall of the second fixed groove, and is fixedly connected to the second positioning plate. In this embodiment, because the second fixed bracket and the second housing are fastened to each other, the second housing moves with the second fixed bracket, and the rotating mechanism may control a motion trail of the second housing by controlling a motion trail of the second fixed bracket. 
     In a possible implementation, the second housing has a second supporting surface, and the second positioning plate sinks relative to the second supporting surface to form a second accommodating groove. The second accommodating groove can provide an accommodation and movement space for the second supporting plate. A location at which the second accommodating groove is disposed enables a supporting surface of the second supporting plate disposed in the second accommodating groove to be flush with the second supporting surface of the second housing. In this way, the second supporting plate can better support the flexible display. A depth of the second accommodating groove is very shallow, and the supporting backplane with high hardness is disposed on the non-display side of the flexible display. Therefore, when the second supporting plate partially extends out of the second accommodating groove, a part that is of the flexible display and that faces the second accommodating groove does not deform significantly when been pressed by a user. This also ensures reliability of the flexible display. 
     In a possible implementation, the fourth fixed bracket is located between the second positioning plate and the groove bottom wall of the second fixed groove, and is fixedly connected to the second positioning plate. A gap is formed between the two second fixed brackets and the fourth fixed bracket, and the groove bottom wall of the second fixed groove, and the gap is used to provide an accommodation and movement space for the second shielding plate. 
     According to a second aspect, this application further provides an electronic device, including a flexible display and the folding apparatus according to any one of the foregoing implementations. The flexible display includes a first non-bending part, a bending part, and a second non-bending part that are sequentially arranged, the first non-bending part is fastened to a first housing, the second non-bending part is fastened to a second housing, and when the first housing and the second housing are folded or unfolded relative to each other, the bending part deforms. 
     In this application, the flexible display can be unfolded or folded with the folding apparatus. When the electronic device is in a flattened state, the flexible display is in a flattened form, and can perform full-screen display, so that the electronic device has a large display area, to improve viewing experience of a user. When the electronic device is in the closed state, a planar size of the electronic device is small (with a small width), so that it is convenient for a user to carry and place the electronic device. 
     In other words, the folding apparatus can implement pulling-in of the housing when the folding apparatus is switched from the flattened state to the closed state and pushing-out of the housing when the folding apparatus is switched from the closed state to the flattened state, to implement deformation by using the flexible display as a neutral surface when being unfolded or folded. In this way, a risk that the flexible display is stretched or squeezed is reduced, to protect the flexible display and improve reliability of the flexible display, so that the flexible display and the electronic device have long service lives. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of a structure in which an electronic device is in a flattened state according to an embodiment of this application; 
         FIG.  2    is a schematic diagram of a structure of a folding apparatus of the electronic device shown in  FIG.  1   ; 
         FIG.  3    is a schematic diagram of a structure in which the electronic device shown in  FIG.  1    is in an intermediate state; 
         FIG.  4    is a schematic diagram of a structure of a folding apparatus of the electronic device shown in  FIG.  3   ; 
         FIG.  5    is a schematic diagram of a structure in which the electronic device shown in  FIG.  1    is in a closed state; 
         FIG.  6    is a schematic diagram of a structure of a folding apparatus of the electronic device shown in  FIG.  5   ; 
         FIG.  7    is a schematic diagram of a partially-exploded structure of the folding apparatus shown in  FIG.  2   ; 
         FIG.  8    is a schematic diagram of a partially-exploded structure of a rotating mechanism shown in  FIG.  7   ; 
         FIG.  9    is a schematic diagram of a structure of the folding apparatus shown in  FIG.  2    from another angle; 
         FIG.  10    is a schematic diagram of a partially-exploded partial structure of the folding apparatus shown in  FIG.  2   ; 
         FIG.  11    is a schematic diagram of an exploded structure of a main shaft assembly shown in  FIG.  10   ; 
         FIG.  12    is a schematic diagram of a structure of a main outer shaft shown in  FIG.  11    from another angle; 
         FIG.  13    is a schematic diagram of a structure in which a main shaft assembly shown in  FIG.  10    is cut along a line A-A; 
         FIG.  14    is a schematic diagram of a structure in which a main shaft assembly shown in  FIG.  10    is cut along a line B-B; 
         FIG.  15    is a schematic diagram of a structure in which a main shaft assembly shown in  FIG.  10    is cut along a line C-C; 
         FIG.  16    is a schematic diagram of a structure in which a main shaft assembly shown in  FIG.  10    is cut along a line D-D; 
         FIG.  17    is a schematic diagram of a structure in which a main shaft assembly shown in  FIG.  10    is cut along a line E-E; 
         FIG.  18    is a schematic diagram of a structure of an end connecting assembly shown in  FIG.  10    from another angle; 
         FIG.  19    is a schematic diagram of a partially-exploded structure of the end connecting assembly shown in  FIG.  18   ; 
         FIG.  20    is a schematic diagram of an exploded structure of a first fixed bracket of the end connecting assembly shown in  FIG.  19   ; 
         FIG.  21    is a schematic diagram of an exploded structure of a second fixed bracket of the end connecting assembly shown in  FIG.  19   ; 
         FIG.  22    is a schematic diagram of a structure of a first limiting component of the end connecting assembly shown in  FIG.  19   ; 
         FIG.  23    is a schematic diagram of an exploded structure of a first limiting component shown in  FIG.  22   ; 
         FIG.  24    is a schematic diagram of a structure of a first transmission arm of the end connecting assembly shown in  FIG.  19   ; 
         FIG.  25    is a schematic diagram of a structure of a first rotating arm of the end connecting assembly shown in  FIG.  19   ; 
         FIG.  26    is a schematic diagram of a structure of a first synchronous swing arm of the end connecting assembly shown in  FIG.  19   ; 
         FIG.  27    is a schematic diagram of a structure of a middle connecting assembly shown in  FIG.  10    from another angle; 
         FIG.  28    is a schematic diagram of an exploded structure of the middle connecting assembly shown in  FIG.  27   ; 
         FIG.  29    is a schematic diagram of a partial structure of a rotating mechanism shown in  FIG.  7   ; 
         FIG.  30    is a schematic diagram of a partial structure of the folding apparatus shown in  FIG.  2   ; 
         FIG.  31    is a schematic diagram of a partial structure of the folding apparatus shown in  FIG.  2   ; 
         FIG.  32    is a schematic diagram of a connection relationship between a partial structure of an end connecting assembly and a main shaft assembly shown in  FIG.  8   ; 
         FIG.  33    is a schematic cross-sectional diagram of a structure of a position that is of a first transmission arm and that is corresponding to the folding apparatus shown in  FIG.  2   ; 
         FIG.  34    is a schematic cross-sectional diagram of a structure of a position that is of a first transmission arm and that is corresponding to the folding apparatus shown in  FIG.  4   ; 
         FIG.  35    is a schematic cross-sectional diagram of a structure of a position that is of a first transmission arm and that is corresponding to the folding apparatus shown in  FIG.  6   ; 
         FIG.  36    is a schematic cross-sectional diagram of a structure of a position that is of a first rotating arm and that is corresponding to the folding apparatus shown in  FIG.  2   ; 
         FIG.  37    is a schematic cross-sectional diagram of a structure of a position that is of a first rotating arm and that is corresponding to the folding apparatus shown in  FIG.  4   ; 
         FIG.  38    is a schematic cross-sectional diagram of a structure of a position that is of a first rotating arm and that is corresponding to the folding apparatus shown in  FIG.  6   ; 
         FIG.  39    is a schematic cross-sectional diagram of a structure of a position of a second transmission arm corresponding to the folding apparatus shown in  FIG.  2   ; 
         FIG.  40    is a schematic cross-sectional diagram of a structure of a position of a second transmission arm corresponding to the folding apparatus shown in  FIG.  4   ; 
         FIG.  41    is a schematic cross-sectional diagram of a structure of a position of a second transmission arm corresponding to the folding apparatus shown in  FIG.  6   ; 
         FIG.  42    is a schematic cross-sectional diagram of a structure of a position that is of a second rotating arm and that is corresponding to the folding apparatus shown in  FIG.  2   ; 
         FIG.  43    is a schematic cross-sectional diagram of a structure of a position that is of a second rotating arm and that is corresponding to the folding apparatus shown in  FIG.  4   ; 
         FIG.  44    is a schematic cross-sectional diagram of a structure of a position that is of a second rotating arm and that is corresponding to the folding apparatus shown in  FIG.  6   ; 
         FIG.  45    is a schematic cross-sectional diagram of a structure of positions that are of a first synchronous swing arm and a second synchronous swing arm and that are corresponding to the folding apparatus shown in  FIG.  2   ; 
         FIG.  46    is a schematic cross-sectional diagram of a structure of positions that are of a first synchronous swing arm and a second synchronous swing arm and that are corresponding to the folding apparatus shown in  FIG.  4   ; and 
         FIG.  47    is a schematic cross-sectional diagram of a structure of positions that are of a first synchronous swing arm and a second synchronous swing arm and that are corresponding to the folding apparatus shown in  FIG.  6   . 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The following describes embodiments of this application with reference to the accompanying drawings in the embodiments of this application. 
     Embodiments of this application provide a folding apparatus and an electronic device. The electronic device includes the folding apparatus and a flexible display fastened to the folding apparatus. The folding apparatus may be unfolded to a flattened state, or may be folded to a closed state, or may be in an intermediate state between the flattened state and the closed state. The flexible display is unfolded and folded with the folding apparatus. In the electronic device, a rotating mechanism of the folding apparatus is optimized, so that the folding apparatus can rotate by using the flexible display as a neutral surface. In this way, a risk that the flexible display is stretched or squeezed is reduced, to protect the flexible display and improve reliability of the flexible display, so that the flexible display and the electronic device have long service lives. 
       FIG.  1    is a schematic diagram of a structure in which an electronic device  1000  is in a flattened state according to an embodiment of this application,  FIG.  2    is a schematic diagram of a structure of a folding apparatus  100  of the electronic device  1000  shown in  FIG.  1   ,  FIG.  3    is a schematic diagram of a structure in which the electronic device  1000  shown in  FIG.  1    is in an intermediate state,  FIG.  4    is a schematic diagram of a structure of the folding apparatus  100  of the electronic device  1000  shown in  FIG.  3   ,  FIG.  5    is a schematic diagram of a structure in which the electronic device  1000  shown in  FIG.  1    is in a closed state, and  FIG.  6    is a schematic diagram of a structure of a folding apparatus  100  of the electronic device  1000  shown in  FIG.  5   . The electronic device  1000  may be a product such as a mobile phone, a tablet computer, or a notebook computer. This embodiment is described by using an example in which the electronic device  1000  is a mobile phone. 
     The electronic device  1000  includes the folding apparatus  100  and a flexible display  200 . The folding apparatus  100  includes a first housing  10 , a rotating mechanism  20 , and a second housing  30  that are sequentially connected. The rotating mechanism  20  can deform, so that the first housing  10  and the second housing  30  are folded or unfolded relative to each other. As shown in  FIG.  1    and  FIG.  2   , the first housing  10  and the second housing  30  can be unfolded relative to each other to a flattened state, so that the electronic device  1000  is in a flattened state. For example, when the first housing  10  and the second housing  30  are in the flattened state, an included angle between the first housing  10  and the second housing  30  may be approximately 180° (a slight deviation is allowed, for example, the included angle is 165°, 177°, or 185°). As shown in  FIG.  3    and  FIG.  4   , the first housing  10  and the second housing  30  can be rotated (unfolded or folded) relative to each other to an intermediate state, so that the electronic device  1000  is in an intermediate state. As shown in  FIG.  5    and  FIG.  6   , the first housing  10  and the second housing  30  can be folded relative to each other to a closed state, so that the electronic device  1000  is in a closed state. For example, when the first housing  10  and the second housing  30  are in the closed state, the first housing  10  and the second housing  30  can be completely closed to be parallel to each other (a slight deviation is also allowed). The intermediate state shown in  FIG.  3    and  FIG.  4    may be any state between the flattened state and the closed state. Therefore, the electronic device  1000  may be switched between the flattened state and the closed state through deformation of the rotating mechanism  20 . 
     In some embodiments, the flexible display  200  is configured to display an image. For example, the flexible display  200  may be an organic light-emitting diode (organic light-emitting diode, OLED) display, an active-matrix organic light-emitting diode (active-matrix organic light-emitting diode, AMOLED) display, a mini light-emitting diode (mini organic light-emitting diode) display, a micro light-emitting diode (micro organic light-emitting diode) display, a micro organic light-emitting diode (micro organic light-emitting diode) display, or a quantum dot light-emitting diode (quantum dot light-emitting diodes, QLED) display. 
     The flexible display  200  includes a first non-bending part  2001 , a bending part  2002 , and a second non-bending part  2003  that are sequentially arranged. The flexible display  200  is fastened to the folding apparatus  100 . For example, the flexible display  200  may be bonded to the folding apparatus  100  by using an adhesive layer. The first non-bending part  2001  of the flexible display  200  is fastened to the first housing  10 , and the second non-bending part  2003  is fastened to the second housing  30 . When the first housing  10  and the second housing  30  are folded or unfolded relative to each other, the bending part  2002  deforms. As shown in  FIG.  1   , when the first housing  10  and the second housing  30  are in the flattened state, the flexible display  200  is in a flattened form. As shown in  FIG.  3   , when the first housing  10  and the second housing  30  are in the intermediate state, the flexible display  200  is in an intermediate form between the flattened form and a closed form. As shown in  FIG.  5   , when the first housing  10  and the second housing  30  are in the closed state, the flexible display  200  is in the closed form. When the electronic device  1000  is in the closed state, the flexible display  200  is located on an outer side of the folding apparatus  100 , and the flexible display  200  may be approximately U-shaped. 
     In this embodiment, the flexible display  200  can be unfolded or folded with the folding apparatus  100 . When the electronic device  1000  is in the flattened state, the flexible display  200  is in the flattened form, and can perform full-screen display, so that the electronic device  1000  has a large display area, to improve viewing experience of a user. When the electronic device  1000  is in the closed state, a planar size of the electronic device  1000  is small (with a small width), so that it is convenient for a user to carry and place the electronic device  1000 . 
     It may be understood that this embodiment is described by using an example in which “a rotation center of the electronic device  1000  is parallel to a width direction of the electronic device  1000 ”. In this case, the electronic device  1000  can rotate leftward and rightward, and folding and unfolding of the electronic device  1000  affect a width of the electronic device  1000 . In some other embodiments, a rotation center of the electronic device  1000  may alternatively be parallel to a length direction of the electronic device  1000 . In this case, the electronic device  1000  can rotate up and down, and folding and unfolding of the electronic device  1000  affect a length of the electronic device  1000 . 
       FIG.  7    is a schematic diagram of a partially-exploded structure of the folding apparatus  100  shown in  FIG.  2   , and  FIG.  8    is a schematic diagram of a partially-exploded structure of a rotating mechanism  20  shown in  FIG.  7   . Fasteners in the folding apparatus  100  are not shown in the accompanying drawings of this application, to simplify the drawings and show a main structure of the folding apparatus  100  more clearly. 
     In some embodiments, the rotating mechanism  20  of the folding apparatus  100  includes a main shaft assembly  1 , an end connecting assembly  20   a , a middle connecting assembly  20   b , a first supporting plate  21 , a second supporting plate  22 , a first shielding plate  23 , and a second shielding plate  24 . 
     The main shaft assembly  1  is located between the first housing  10  and the second housing  30 . The end connecting assembly  20   a  is connected to the first housing  10 , the main shaft assembly  1 , and the second housing  30 . There are two end connecting assemblies  20   a , and the two end connecting assemblies  20   a  are spaced in an axial direction of the main shaft assembly  1 , for example, may be respectively connected to the top and the bottom of the main shaft assembly  1 . The middle connecting assembly  20   b  is connected to the first housing  10 , the main shaft assembly  1 , and the second housing  30 . The middle connecting assembly  20   b  is located between the two end connecting assemblies  20   a . The first supporting plate  21  and the second supporting plate  22  are located on one side of a plurality of connecting assemblies (that is, the two end connecting assemblies  20   a  and the middle connecting assembly  20   b ), and the first shielding plate  23  and the second shielding plate  24  are located on the other side of the plurality of connecting assemblies (the assemblies  20   a  and the assembly  20   b ). 
     The first supporting plate  21  is located on a side that is of the main shaft assembly  1  and that faces the first housing  10 , and the first supporting plate  21  is connected to the end connecting assemblies  20   a . In some embodiments, the first supporting plate  21  may alternatively be connected to the middle connecting assembly  20   b . The second supporting plate  22  is located on a side that is of the main shaft assembly  1  and that faces the second housing  30 , and the second supporting plate  22  is connected to the end connecting assemblies  20   a . In some embodiments, the second supporting plate  22  may alternatively be connected to the middle connecting assembly  20   b . 
     The first housing  10  has a first supporting surface  101 , and the first supporting surface  101  is configured to support the flexible display  200 . The second housing  30  has a second supporting surface  301 , and the second supporting surface  301  is configured to support the flexible display  200 . When the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, the first supporting surface  101  is flush with the second supporting surface  301 , to better support the flexible display  200 , so that the flexible display  200  is flatter, improving user experience. 
     The main shaft assembly  1  has a supporting surface  11 . When the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, the supporting surface  11  of the main shaft assembly  1  is partially exposed relative to the first supporting plate  21  and the second supporting plate  22 . The first supporting plate  21 , the main shaft assembly  1 , and the second supporting plate  22  can jointly support the bending part  2002  of the flexible display  200 , so that the flexible display  200  is flatter and is not easily damaged due to an external force touch, improving reliability of the flexible display  200 . As shown in  FIG.  4   , when the first housing  10  and the second housing  30  are in the intermediate state, the supporting surface  11  of the main shaft assembly  1  is partially exposed relative to the first supporting plate  21  and the second supporting plate  22 , an exposed area of the supporting surface  11  of the main shaft assembly  1  is larger than an exposed area in the flattened state, and the supporting surface  11  of the main shaft assembly  1 , the first supporting plate  21 , and the second supporting plate  22  jointly support the bending part  2002  of the flexible display  200 . As shown in  FIG.  6   , when the first housing  10  and the second housing  30  are folded relative to each other to the closed state, the supporting surface  11  of the main shaft assembly  1  is completely exposed relative to the first supporting plate  21  and the second supporting plate  22 , and the supporting surface  11  of the main shaft assembly  1  supports the bending part  2002  of the flexible display  200 . 
     For example, the supporting surface  11  of the main shaft assembly  1  is arc-shaped. In this case, when the first housing  10  and the second housing  30  are folded relative to each other to a closed state, the main shaft assembly  1  can provide complete-semicircle or nearly-semicircle support for the bending part  2002  of the flexible display  200 , and this is consistent with an ideal closed form of the bending part  2002  of the flexible display  200 , so that more optimized support can be provided for the flexible display  200  in the closed form. A central angle of the supporting surface  11  of the main shaft assembly  1  may be within a range of 150° to 180°, to better support the flexible display  200 . 
     It may be understood that, in this embodiment of this application, there are two cases in which the supporting surface  11  of the main shaft assembly  1  is arc-shaped. One is that the supporting surface  11  of the main shaft assembly  1  is standard-arc-shaped, and the other is that the entire supporting surface  11  of the main shaft assembly  1  is approximately arc-shaped. In some other embodiments, the supporting surface  11  of the main shaft assembly  1  may alternatively have another shape. For example, the supporting surface  11  of the main shaft assembly  1  is set to a semi-ellipse shape, to reduce a width of the folding apparatus  100  in the closed state, so that it is more convenient to carry and place the electronic device. A shape of the supporting surface of the main shaft assembly  1  is not strictly limited in this embodiment of this application. 
       FIG.  9    is a schematic diagram of a structure of the folding apparatus  100  shown in  FIG.  2    from another angle. A view angle of the folding apparatus  100  in  FIG.  9    is a view angle obtained after a view angle of the folding apparatus  100  in  FIG.  2    is turned over. 
     In some embodiments, the first shielding plate  23  is located on the side that is of the main shaft assembly  1  and that faces the first housing  10 , and the first shielding plate  23  is connected to the end connecting assemblies  20   a . In some embodiments, the first shielding plate  23  may alternatively be connected to the middle connecting assembly  20   b . The second shielding plate  24  is located on the side that is of the main shaft assembly  1  and that faces the second housing  30 , and the second shielding plate  24  is connected to the end connecting assemblies  20   a . In some embodiments, the second shielding plate  24  may alternatively be connected to the middle connecting assembly  20   b . 
     The main shaft assembly  1  has a shielding surface  12 . When the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, the shielding surface  12  of the main shaft assembly  1  is exposed relative to the first shielding plate  23  and the second shielding plate  24 . The first shielding plate  23  is located between the first housing  10  and the main shaft assembly  1 , and can shield a gap between the first housing  10  and the main shaft assembly  1 . The second shielding plate  24  is located between the second housing  30  and the main shaft assembly  1 , and can shield a gap between the second housing  30  and the main shaft assembly  1 . Therefore, the first shielding plate  23 , the main shaft assembly  1 , and the second shielding plate  24  can jointly shield a gap between the first housing  10  and the second housing  30 , so that the rotating mechanism  20  can implement self-shielding in the flattened state. In this way, appearance integrity is improved, and a risk that dust, sundries, and the like enter the rotating mechanism  20  from outside can also be lowered, to ensure reliability of the folding apparatus  100 . 
       FIG.  10    is a schematic diagram of a partially-exploded partial structure of the folding apparatus  100  shown in  FIG.  2   . 
     In some embodiments, a plurality of movement spaces communicating with the outside of the main shaft assembly  1  are formed inside the main shaft assembly  1 , and the plurality of connecting assemblies (the assemblies  20   a  and the assembly  20   b ) of the rotating mechanism  20  are movably disposed in these movement spaces to connect to the main shaft assembly  1 . A rotation center of the entire rotating mechanism  20  is parallel to the axial direction of the main shaft assembly  1 , and the main shaft assembly  1  extends in the axial direction of the main shaft assembly  1 . 
     In some embodiments, structures of the two end connecting assemblies  20   a  are mirror-symmetrical with each other. In this case, the structures of the two end connecting assemblies  20   a  are the same, so that an overall structure of the rotating mechanism  20  is simple and processing costs are low. Because the two end connecting assemblies  20   a  are mirror-symmetrically arranged, in a rotation process of the folding apparatus  100 , stress between the two end connecting assemblies  20   a  and the main shaft assembly  1 , between the two end connecting assemblies  20   a  and the first housing  10 , and between the two end connecting assemblies  20   a  and the second housing  30  are even. This helps improve reliability of the folding apparatus  100 . In some other embodiments, structures of the two end connecting assemblies  20   a  may alternatively be different. 
     A structure of the middle connecting assembly  20   b  is simpler than the structure of the end connecting assembly  20   a . In the rotating mechanism  20 , the two end connecting assemblies  20   a  implement primary connection and control functions, and the middle connecting assembly  20   b  implements secondary connection and control functions. In some other embodiments, the rotating mechanism  20  may not be provided with the middle connecting assembly  20   b . In some other embodiments, alternatively, in the rotating mechanism  20 , a middle connecting assembly may be set to a primary connecting assembly (for example, for a structure of the connecting assembly, refer to the structure of the end connecting assembly  20   a  in  FIG.  10   ), and an end connecting assembly may be set to a secondary connecting assembly (for example, for a structure of the connecting assembly, refer to the structure of the middle connecting assembly  20   b  in  FIG.  10   ). In some other embodiments, in this embodiment of this application, only one end connecting assembly  20   a  may be disposed, and the end connecting assembly  20   a  is connected to the middle of the main shaft assembly  1 , the middle of the first housing  10 , and the middle of the second housing  30 . It may be understood that the structure of the rotating mechanism  20  may have a plurality of combination and variation manners. This is not strictly limited in this embodiment of this application. 
       FIG.  11    is a schematic diagram of an exploded structure of the main shaft assembly  1  shown in  FIG.  10   .  FIG.  12    is a schematic diagram of a structure of a main outer shaft  14  shown in  FIG.  11    from another angle. 
     In some embodiments, the main shaft assembly  1  includes the main outer shaft  14 , a main inner shaft  15 , and a shielding plate  16 . The main outer shaft  14  is fastened on one side of the main inner shaft  15 , and the shielding plate  16  is fastened on the other side of the main inner shaft  15 . The supporting surface  11  of the main shaft assembly  1  is formed on the main outer shaft  14 , and is disposed to face away from the main inner shaft  15 . The shielding surface  12  of the main shaft assembly  1  is formed on the shielding plate  16 , and is disposed to face away from the main outer shaft  14 . In some embodiments, the shielding plate  16  and the main inner shaft  15  may be fastened to each other in an assembled manner. In some other embodiments, the shielding plate  16  and the main inner shaft  15  may be alternatively an integrally-formed mechanical part. 
     A plurality of three-dimensional space structures are disposed on both the main inner shaft  15  and the main outer shaft  14 . These structures are designed, so that after the main inner shaft  15  and the main outer shaft  14  are assembled, the main inner shaft  15  and the main outer shaft  14  can jointly form a plurality of movement spaces, and mechanical parts of the plurality of connecting assemblies (the assemblies  20   a  and the assembly  20   b ) are movably disposed in the plurality of movement spaces of the main shaft assembly  1 , to implement connection to the main shaft assembly  1 . A split design of the main inner shaft  15  and the main outer shaft  14  helps reduce manufacturing difficulty of the main shaft assembly  1 , and improve manufacturing precision and a product yield of the main shaft assembly  1 . 
     In some embodiments, as shown in  FIG.  11   , the main inner shaft  15  includes a main inner shaft body  151 , a plurality of grooves  152 , a plurality of projections  153 , two end stoppers  154  and a plurality of fastening holes  155 . The plurality of grooves  152  and the plurality of projections  153  are formed on the main inner shaft body  151 , and the plurality of grooves  152  and the plurality of projections  153  are combined with each other to form a plurality of three-dimensional spatial structures. The two end stoppers  154  are fastened at two ends of the main inner shaft body  151 . The plurality of fastening holes  155  are formed on the main inner shaft body  151 . Some grooves  152 , some projections  153 , and some fastening holes  155  are schematically marked in  FIG.  11   . 
     As shown in  FIG.  12   , the main outer shaft  14  includes a main outer shaft body  141 , two limiting flanges  142 , a plurality of grooves  143 , a plurality of projections  144 , and a plurality of fastening holes  145 . The two limiting flanges  142  are spaced from each other and respectively fixed on two sides of the main outer shaft body  141 , and the limiting flanges  142  extend along an extension direction of the main shaft assembly  1 . The plurality of grooves  143  and the plurality of projections  144  are formed on the main outer shaft body  141 , and the plurality of grooves  143  and the plurality of projections  144  are combined with each other to form a plurality of three-dimensional spatial structures. The plurality of fastening holes  145  are formed on the main outer shaft body  141 . Some grooves  143 , some projections  144 , and some fastening holes  145  are schematically marked in  FIG.  12   . 
     After the main outer shaft  14  and the main inner shaft  15  are fastened to each other, the main outer shaft body  141  and the main inner shaft body  151  are in contact with each other, the end stoppers  154  of the main inner shaft  15  are exposed. The plurality of fastening holes  155  of the main outer shaft  14  are aligned with the plurality of fastening holes  145  of the main inner shaft  15 , and the main inner shaft  15  and the main outer shaft  14  are fastened by using fasteners (not shown in the figure). The fastener includes but is not limited to a screw, a bolt, a rivet, a dowel pin, and the like. The plurality of three-dimensional space structures of the main outer shaft  14  and the plurality of three-dimensional space structures of the main inner shaft  15  jointly form the plurality of movement spaces of the main shaft assembly  1 . For example, some of the plurality of movement spaces are the same in structure, and some of the plurality of movement spaces are different in structure. The movement spaces with different structures are used to cooperate with mechanical parts with different structures, so that connection structures between the main shaft assembly  1  and the plurality of connecting assemblies (the assemblies  20   a  and the assembly  20   b ) are more flexible and diversified. The movement spaces with a same structure are used to cooperate with mechanical parts with a same structure, which helps reduce design difficulty and costs of the main shaft assembly  1  and the connecting assemblies. 
     In some embodiments, as shown in  FIG.  11   , some projections  153  of the main inner shaft  15  have limiting grooves  1531 , configured to limit, in the axial direction of the main shaft assembly  1 , a mechanical part disposed in a corresponding movement space, to improve reliability of a connection structure. Some limiting grooves  1531  are schematically marked in  FIG.  11   . As shown in  FIG.  12   , limiting grooves  1431  are disposed on groove walls of some grooves  143  of the main outer shaft  14 , configured to limit, in the axial direction of the main shaft assembly  1 , a mechanical part disposed in a corresponding movement space, to improve reliability of a connection structure. Some limiting grooves  1431  are schematically marked in  FIG.  12   . It may be understood that when one limiting groove ( 1531 / 1431 ) is disposed in a same movement space, a mechanical part can be limited in the axial direction of the main shaft assembly  1 . In some other embodiments, two limiting grooves ( 1531  and  1431 ) may alternatively be disposed in a same movement space. This is not strictly limited in this embodiment of this application. 
     In some embodiments, as shown in  FIG.  12   , some projections  144  of the main outer shaft  14  have a limiting function. These projections  144  are located in the movement spaces of the main shaft assembly  1 , and are configured to limit mechanical parts of the connecting assemblies (the assemblies  20   a  and the assembly  20   b ), to prevent the mechanical parts from accidentally detaching from the main shaft assembly  1 , so as to improve reliability of connection and motion between the connecting assemblies (the assemblies  20   a  and the assembly  20   b ) and the main shaft assembly  1 , so that reliability of the rotating mechanism  20  and the folding apparatus  100  are higher. It may be understood that, in the main shaft assembly  1 , a projection may alternatively be disposed on the main inner shaft  15  for a limiting function. 
       FIG.  13    is a schematic diagram of a structure in which the main shaft assembly  1  shown in  FIG.  10    is cut along a line A-A,  FIG.  14    is a schematic diagram of a structure in which the main shaft assembly  1  shown in  FIG.  10    is cut along a line B-B,  FIG.  15    is a schematic diagram of a structure in which the main shaft assembly  1  shown in  FIG.  10    is cut along a line C-C,  FIG.  16    is a schematic diagram of a structure in which the main shaft assembly  1  shown in  FIG.  10    is cut along a line D-D, and  FIG.  17    is a schematic diagram of a structure in which the main shaft assembly  1  shown in  FIG.  10    is cut along a line E-E. 
     For example, in this embodiment, there are a plurality of movement spaces with different shapes formed on the main shaft assembly  1 , configured to cooperate with different mechanical parts. 
     As shown in  FIG.  13   , the main outer shaft  14  and the main inner shaft  15  jointly enclose an arc-shaped groove  131 . A circle center of the arc-shaped groove  131  is close to the main inner shaft  15  and away from the main outer shaft  14 , to form a movement space. In some embodiments, the movement space may further include a limiting groove  1531  communicating with the arc-shaped groove  131 . The limiting groove  1531  is formed on the main inner shaft  13 . In some embodiments, the main outer shaft  14  may further include a projection  144  having a limiting function, and the projection  144  extends into the arc-shaped groove  131  to limit a mechanical part disposed in the movement space. 
     As shown in  FIG.  14   , the main outer shaft  14  and the main inner shaft  15  jointly enclose an arc-shaped groove  131 . A circle center of the arc-shaped groove  131  is close to the main inner shaft  15  and away from the main outer shaft  14 , to form a movement space. The arc-shaped groove  131  shown in  FIG.  13    and the arc-shaped groove  131  shown in  FIG.  14    are disposed in pairs. In some embodiments, the movement space may further include a limiting groove  1531  communicating with the arc-shaped groove  131 . The limiting groove  1531  is formed on the main inner shaft  15 . In some embodiments, the main outer shaft  14  may further include a projection  144  having a limiting function, and the projection  144  extends into the arc-shaped groove  131  to limit a mechanical part disposed in the movement space. 
     As shown in  FIG.  15   , the main outer shaft  14  and the main inner shaft  15  jointly enclose an arc-shaped groove  131 . A circle center of the arc-shaped groove  131  is close to the main outer shaft  14  and away from the main inner shaft  15 , to form a movement space. In some embodiments, the movement space may further include a limiting groove  1431  communicating with the arc-shaped groove  131 . The limiting groove  1431  is formed on the main outer shaft  14 . In some embodiments, the main outer shaft  14  may further include a projection  144  having a limiting function, and the projection  144  extends into the arc-shaped groove  131  to limit a mechanical part disposed in the movement space. 
     As shown in  FIG.  16   , the main outer shaft  14  and the main inner shaft  15  jointly enclose an arc-shaped groove  131 . A circle center of the arc-shaped groove  131  is close to the main outer shaft  14  and away from the main inner shaft  15 , to form a movement space. The arc-shaped groove  131  shown in  FIG.  15    and the arc-shaped groove  131  shown in  FIG.  16    are disposed in pairs. In some embodiments, the movement space may further include a limiting groove  1431  communicating with the arc-shaped groove  131 . The limiting groove  1431  is formed on the main outer shaft  14 . In some embodiments, the main outer shaft  14  may further include a projection  144  having a limiting function, and the projection  144  extends into the arc-shaped groove  131  to limit a mechanical part disposed in the movement space. 
     In other words, the main inner shaft  15  and the main outer shaft  14  of the main shaft assembly  1  jointly enclose a plurality of arc-shaped grooves  131 . The arc-shaped grooves  131  at different locations may be connected to different mechanical parts of the connecting assemblies (the assemblies  20   a  and the assembly  20   b ). 
     As shown in  FIG.  17   , the main outer shaft  14  and the main inner shaft  15  jointly enclose an M-shaped groove  132 , two spaced recess grooves  133  are formed on a side wall of the M-shaped groove  132 , and the M-shaped groove  132  and the two recess grooves  133  jointly form a movement space. 
     It may be understood that the main shaft assembly  1  in this embodiment of this application may alternatively have another structure. This is not strictly limited in this application. 
       FIG.  18    is a schematic diagram of a structure of the end connecting assembly  20   a  shown in  FIG.  10    from another angle, and  FIG.  19    is a schematic diagram of a partially-exploded structure of the end connecting assembly  20   a  shown in  FIG.  18   . 
     In some embodiments, the end connecting assembly  20   a  of the rotating mechanism  20  includes a first fixed bracket  31 , a second fixed bracket  32 , a first transmission arm  4 , a first rotating arm  5 , a second transmission arm  6 , and a second rotating arm  7 . In some embodiments, the rotating mechanism  20  may further include a first limiting component  81  and a second limiting component  82 . In some embodiments, the rotating mechanism  20  may further include a first synchronous swing arm  91  and a second synchronous swing arm  92 . 
       FIG.  20    is a schematic diagram of an exploded structure of the first fixed bracket  31  of the end connecting assembly  20   a  shown in  FIG.  19   . 
     In some embodiments, the first fixed bracket  31  includes a first fixed base  311  and a first fastener  312 . The first fastener  312  is fastened to the first fixed base  311 , and encloses a first arc-shaped groove  313  with the first fixed base  311 . For example, the first fastener  312  and the first fixed base  311  may be fastened to each other by using a fastener. 
     In this embodiment, a processing manner is used in which the first fixed base  311  and the first fastener  312  are separately manufactured, and then the first fixed base  311  and the first fastener  312  are assembled into the first fixed bracket  31 . This helps reduce processing difficulty of the first fixed bracket  31 , and improve a product yield of the first fixed bracket  31 . In some other embodiments, the first fixed bracket  31  may alternatively be an integrally-formed mechanical part. 
     In some embodiments, as shown in  FIG.  20   , the first fastener  312  has an arc surface used to enclose the first arc-shaped groove  313 , and a limiting groove  3121  is formed on a middle part of the arc surface and configured to limit, in an axial direction of the main shaft assembly  1 , a mechanical part disposed in the first arc-shaped groove  313 , to improve reliability of a connection structure. In some other embodiments, the limiting groove may alternatively be formed on an arc surface that is of the first fixed base  311  and that is used to enclose the first arc-shaped groove  313 . For example, the first fastener  312  may further have a stop block  3122 , configured to prevent the mechanical part disposed in the first arc-shaped groove  313  from being accidentally detached from the first arc-shaped groove  313 . 
     As shown in  FIG.  20   , in some embodiments, there may be further a first sliding slot  314  and a first accommodating slot  315  on the first fixed base  311  of the first fixed bracket  31 , and the first accommodating slot  315  communicates with the first sliding slot  314 . In some embodiments, there may be a recessed guiding space  3141  on a side wall of the first sliding slot  314 . In some embodiments, there may further be a third sliding slot  316  on the first fixed base  311  of the first fixed bracket  31 , and there is a recessed guiding space  3161  on a slot wall of the third sliding slot  316 . A guiding direction of the guiding space  3161  of the third sliding slot  316  is the same as a guiding direction of the guiding space  3141  of the first sliding slot  314 . 
     It may be understood that, in this embodiment, the first sliding slot  314 , the third sliding slot  316 , and the first arc-shaped groove  313  are all formed on a same mechanical part, and the first fixed base  311  is an integrated mechanical part. In some other embodiments, the first sliding slot  314 , the third sliding slot  316 , and the first arc-shaped groove  313  may alternatively be formed on different mechanical parts, and the first fixed base  311  may include a plurality of mechanical parts. This is not strictly limited in this application. 
     As shown in  FIG.  20   , in some embodiments, the first fixed base  311  of the first fixed bracket  31  has a plurality of fastening holes  3111 . In the rotating mechanism  20 , the first fixed bracket  31  may be fastened to the first housing  10  by using a plurality of fasteners. In some embodiments, the first fixed bracket  31  may further have a positioning projection  3112 , and the positioning projection  3112  is configured to cooperate with the first housing  10 , so that assembly precision and stability of a connection structure between the first fixed bracket  31  and the first housing  10  are higher. 
       FIG.  21    is a schematic diagram of an exploded structure of the second fixed bracket  32  of the end connecting assembly  20   a  shown in  FIG.  19   . 
     In some embodiments, a structure of the second fixed bracket  32  is similar to a structure of the first fixed bracket  31 . For example, the second fixed bracket  32  includes a second fixed base  321  and a second fastener  322 . The second fastener  322  is fastened to the second fixed base  321 , and encloses a second arc-shaped groove  323  with the second fixed base  321 . A structure of the second fastener  322  may be the same as a structure of the first fastener  312 . 
     There may be further a second sliding slot  324  and a second accommodating slot  325  on the second fixed base  321  of the second fixed bracket  32 , and the second accommodating slot  325  communicates with the second sliding slot  324 . There may be a recessed guiding space  3241  on a side wall of the second sliding slot  324 . Structures of the second sliding slot  324  and the second accommodating slot  325  may be the same as structures of the first sliding slot  314  and the first accommodating slot  315  of the first fixed bracket  31 . There may be further a fourth sliding slot  326  on the second fixed base  321  of the second fixed bracket  32 , and there is a recessed guiding space  3261  on a slot wall of the fourth sliding slot  326 . A structure of the fourth sliding slot  326  may be the same as a structure of the second sliding slot  324  of the first fixed bracket  31 . 
     Locations of a plurality of slots on the second fixed bracket  32  may be different from locations of a plurality of slots on the first fixed bracket  31 . For example, the plurality of slots on the second fixed bracket  32  may be staggered with the plurality of slots on the first fixed bracket  31  in a direction parallel to the axial direction the main shaft assembly  1 , so that a plurality of mechanical parts connected to the second fixed bracket  32  and the first fixed bracket  31  can be arranged in the axial direction of the main shaft assembly  1 , to improve space utilization of the rotating mechanism  20 . 
       FIG.  22    is a schematic diagram of a structure of the first limiting component  81  of the end connecting assembly  20   a  shown in  FIG.  19   , and  FIG.  23    is a schematic diagram of an exploded structure of the first limiting component  81  shown in  FIG.  22   . 
     In some embodiments, the first limiting component  81  includes a first bracket  811  and a first elastic part  812 . The first bracket  811  is a rigid structure and is not easy to deform under an external force. The first bracket  811  includes a control part  8111  and an abutting part  8112 . The abutting part  8112  is configured to abut against an external mechanical part to limit the mechanical part. The control part  8111  is configured to control a location of the abutting part  8112 . For example, the control part  8111  includes a substrate  8113  and a plurality of guide columns  8114 , and the plurality of guide columns  8114  are fastened on one side of the substrate  8113  and spaced from each other. The abutting part  8112  is fastened on the other side of the substrate  8113 . The first elastic part  812  is an elastic structure and is easy to deform under an external force. One end of the first elastic part  812  is disposed on the control part  8111  of the first bracket  811 . For example, the first elastic part  812  may include a plurality of springs  8121 , and the plurality of springs  8121  are sleeved on the plurality of guide columns  8114  in a one-to-one correspondence. Refer to  FIG.  18   ,  FIG.  20   , and  FIG.  22   . The first limiting component  81  is disposed in the first accommodating slot  315  of the first fixed bracket  31 . The other end (that is, an end away from the control part  8111 ) of the first elastic part  812  abuts against a slot wall of the first accommodating slot  315 , the first elastic part  812  is in a compressed state, and the abutting part  8112  of the first bracket  811  partially extends into the first sliding slot  314 . 
     In some embodiments, the first limiting component  81  may further include a first elastic part  813 , and the first elastic part  813  is disposed on the abutting part  8112  of the first bracket  811 . The first elastic part  813  may be made of a material (for example, rubber) with low rigidity, so that when subject to an external force, the first elastic part  813  can absorb an impact force through deformation, to implement cushioning. In the first limiting component  81 , the first elastic part  813  is disposed to cushion stress between the abutting part  8112  and a mechanical part, to improve reliability of a limiting structure. 
     In some embodiments, the first bracket  811  of the first limiting component  81  may further include a positioning part  8115 . The positioning part  8115  is fastened below the abutting part  8112 , and protrudes relative to the abutting part  8112  in a direction away from the control part  8111 . When a mechanical part abuts against the abutting part  8112 , the positioning part  8115  can position and support the mechanical part, to improve reliability of the limiting structure. 
     In some embodiments, a structure of the second limiting component  82  may be similar to or the same as a structure of the first limiting component  81 , to perform a limiting function. 
       FIG.  24    is a schematic diagram of a structure of the first transmission arm  4  of the end connecting assembly  20   a  shown in  FIG.  19   . 
     In some embodiments, the first transmission arm  4  includes a sliding end  41  and a rotating end  42 , and the sliding end  41  and the rotating end  42  of the first transmission arm  4  are fastened to each other. For example, the first transmission arm  4  may be an integrally-formed mechanical part. 
     In some embodiments, there is a first recessed area  411  and a second recessed area  412  on the sliding end  41  of the first transmission arm  4 , and the second recessed area  412  is located between the first recessed area  411  and the rotating end  42  of the first transmission arm  4 . The sliding end  41  of the first transmission arm  4  includes a first flange  413  on a circumferential side. The first recessed area  411  and the second recessed area  412  are formed on a first flange  413 . 
     Refer to  FIG.  18   ,  FIG.  20   , and  FIG.  24   . The sliding end  41  of the first transmission arm  4  is disposed in the first sliding slot  314 , and the first flange  413  is disposed in the guiding space  3141  of the first sliding slot  314 . In this embodiment, the guiding space  3141  of the first sliding slot  314  cooperates with the first flange  413  of the first transmission arm  4 , so that the sliding end  41  of the first transmission arm  4  can be guided in a sliding direction of the first sliding slot  314 . In this way, a relative sliding action between the first transmission arm  4  and the first fixed bracket  31  is easier to implement and control precision is higher. 
     The first limiting component  81  is clamped to the sliding end  41  of the first transmission arm  4  to limit the first transmission arm  4 , so that the first transmission arm  4  and the first fixed bracket  31  can maintain a preset relative position relationship when no large external force is applied, the rotating mechanism  20  can stay at a preset angle, and the rotating mechanism can maintain the flattened state or the closed state. In this way, user experience of the folding apparatus  100  and the electronic device  1000  is improved. In some embodiments, when the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, the first limiting component  81  is partially clamped into the first recessed area  411 . When the first housing  10  and the second housing  30  are folded relative to each other to the closed state, the first limiting component  81  is partially clamped into the second recessed area  412 . 
     Refer to  FIG.  18   ,  FIG.  23   , and  FIG.  24   . For example, the abutting part  8112  of the first bracket  811  of the first limiting component  81  is clamped to the sliding end  41  of the first transmission arm  4 . Because the first elastic part  812  of the first limiting component  81  can deform under an external force, the first limiting component  81  can smoothly move between the first recessed area  411  and the second recessed area  412  relative to the sliding end  41  of the first transmission arm  4 , to improve reliability of limiting between the first limiting component  81  and the sliding end  41  of the first transmission arm  4 . 
     Because the first elastic part  813  is sleeved on the abutting part  8112  of the first bracket  811 , the first limiting component  81  abuts against the sliding end  41  of the first transmission arm  4  by using the first elastic part  813  having a cushioning function. This helps reduce a risk of wearing the first bracket  811  and the first transmission arm  4  in a long-time relative movement, improve limiting reliability of the first limiting component  81 , and improve reliability of the rotating assembly. 
     For example, two adjacent surfaces of the first flange  413  of the first transmission arm  4  respectively abut the abutting part  8112  of the first bracket  811  and the positioning part  8115  of the first bracket  811 , so that the first flange  413  can slide relative to the positioning part  8115  of the first bracket  811 . The positioning part  8115  of the first bracket  811  is disposed, so that a limiting connection relationship between the first limiting component  81  and the sliding end  41  of the first transmission arm  4  is more reliable, to improve reliability of the rotating assembly. 
     In some embodiments, as shown in  FIG.  24   , the rotating end  42  of the first transmission arm  4  is arc-shaped. Refer to  FIG.  13    and  FIG.  24   . The rotating end  42  of the first transmission arm  4  may be disposed in one of the arc-shaped grooves  131  of the main shaft assembly  1 , so that the first transmission arm  4  is rotatably connected to the main shaft assembly  1 . In this case, a rotation center around which the first transmission arm  4  rotates relative to the main shaft assembly  1  is close to the main inner shaft  15  and away from the main outer shaft  14 . 
     In this embodiment, the first transmission arm  4  is connected to the main shaft assembly  1  by using a virtual shaft. The rotatable connection has a simple structure and occupies small space. This helps reduce a thickness of the rotating mechanism  20 , so that the folding apparatus  100  and the electronic device  1000  are more light and thin. In some other embodiments, the first transmission arm  4  may alternatively be connected to the main shaft assembly  1  by using a physical shaft. This is not strictly limited in this embodiment of this application. 
     The rotating end  42  of the first transmission arm  4  includes a limiting bulge  421  and a limiting projection  422 , and the limiting bulge  421  is formed on an inner side of the rotating end  42  and the limiting projection  422  is formed on an end part of the rotating end  42 . The limiting bulge  421  is configured to cooperate with the limiting groove  1531  (refer to  FIG.  13   ) of the main shaft assembly  1 , so that mutual limiting of the first transmission arm  4  and the main shaft assembly  1  is implemented in the axial direction of the main shaft assembly  1 . The limiting projection  422  is configured to cooperate with the projection  144  (refer to  FIG.  13   ) of the main shaft assembly  1  that has a limiting function, to prevent the first transmission arm  4  from being accidentally detached from the main shaft assembly  1 . 
     In some embodiments, as shown in  FIG.  18    and  FIG.  19   , a structure of the second transmission arm  6  may be the same as a structure of the first transmission arm  4 . The second transmission arm  6  includes a sliding end  61  and a rotating end  62 . The sliding end  61  of the second transmission arm  6  is slidably connected to the second fixed bracket  32 . The sliding end  61  of the second transmission arm  6  may be disposed in the second sliding slot  324  of the second fixed bracket  32 . A second limiting component  82  may be disposed on the second fixed bracket  32 , and the second limiting component  82  is configured to limit a relative motion between the sliding end  61  of the second transmission arm  6  and the second fixed bracket  32 . The rotating end  62  of the second transmission arm  6  is rotatably connected to the main shaft assembly  1 . 
     Refer to  FIG.  14    and  FIG.  19   . The rotating end  62  of the second transmission arm  6  is arc-shaped and is disposed in one of the arc-shaped grooves  131  of the main shaft assembly  1 . In this case, a rotation center around which the second transmission arm  6  rotates relative to the main shaft assembly  1  is close to the main inner shaft  15  and away from the main outer shaft  14 . In this embodiment, the second transmission arm  6  is connected to the main shaft assembly  1  by using a virtual shaft. In some other embodiments, the first transmission arm  4  may alternatively be connected to the main shaft assembly  1  by using a physical shaft. This is not strictly limited in this embodiment of this application. 
       FIG.  25    is a schematic diagram of a structure of the first rotating arm  5  of the end connecting assembly  20   a  shown in  FIG.  19   . 
     In some embodiments, both ends of the first rotating arm  5  are rotating ends. One end  51  that is of the first rotating arm  5  and that is rotatably connected to the first fixed bracket  31  is arc-shaped and is disposed in the first arc-shaped groove  313 . For example, one end  51  of the first rotating arm  5  includes a limiting bulge  511  and a limiting projection  512 . The limiting bulge  511  is configured to cooperate with the limiting groove  3121  of the first arc-shaped groove  313 . The limiting projection  512  is configured to cooperate with the stop block  3122  of the first fixed bracket  31 . 
     Refer to  FIG.  25    and  FIG.  15   . One end  52  that is of the first rotating arm  5  and that is rotatably connected to the main shaft assembly  1  is arc-shaped and is disposed in one of the arc-shaped grooves  131  of the main shaft assembly  1 . In this case, a rotation center around which the first rotating arm  5  rotates relative to the main shaft assembly  1  is close to the main outer shaft  14  and away from the main inner shaft  15 . For example, the end  52  of the first rotating arm  5   includes a limiting bulge  521  and a limiting projection  522 . The limiting bulge  521  is configured to cooperate with the limiting groove  1431  of the main shaft assembly  1 . The limiting projection  522  is configured to cooperate with the limiting projection  144  of the main shaft assembly  1 . 
     In this embodiment, the first rotating arm  5  is approximately in a “W” shape. The first rotating arm  5  is connected to the first fixed bracket  31  by using a virtual shaft, and the first rotating arm  5  is also connected to the main shaft assembly  1  by using a virtual shaft. In this way, the rotatable connection has a simple structure and occupies small space. This helps reduce a thickness of the rotating mechanism  20 , so that the folding apparatus  100  and the electronic device  1000  are more light and thin. In some other embodiments, the first rotating arm  5  may alternatively be connected to the first fixed bracket  31  by using a physical shaft, and the first rotating arm  5  may alternatively be connected to the main shaft assembly  1  by using a physical shaft. This is not strictly limited in this embodiment of this application. 
     In some embodiments, as shown in  FIG.  18    and  FIG.  19   , a structure of the second rotating arm  7  may be the same as a structure of the first rotating arm  5 . Both ends of the second rotating arm  7  are rotating ends. The second rotating arm  7  is approximately in a “W” shape. One end  71  that is of the second rotating arm  7  and that is rotatably connected to the second fixed bracket  32  is arc-shaped and is disposed in the second arc-shaped groove  323 . Refer to  FIG.  16    and  FIG.  19   . One end  72  that is of the second rotating arm  7  and that is rotatably connected to the main shaft assembly  1  is arc-shaped and is disposed in one of the arc-shaped grooves  131  of the main shaft assembly  1 . In this case, a rotation center around which the second rotating arm  7  rotates relative to the main shaft assembly  1  is close to the main outer shaft  14  and away from the main inner shaft  15 . In this embodiment, the second rotating arm  7  is separately connected to the second fixed bracket  32  and the main shaft assembly  1  by using a virtual shaft. In some other embodiments, the second rotating arm  7  may alternatively be separately connected to the second fixed bracket  32  and the main shaft assembly  1  by using a physical shaft. This is not strictly limited in this embodiment of this application. 
       FIG.  26    is a schematic diagram of a structure of the first synchronous swing arm  91  of the end connecting assembly  20   a  shown in  FIG.  19   . 
     In some embodiments, the first synchronous swing arm  91  includes a rotating end  911  and a movable end  912 . The rotating end  911  of the first synchronous swing arm  91  is rotatably connected to the main shaft assembly  1 , and the movable end  912  of the first synchronous swing arm  91  is movably connected to the first fixed bracket  31 . When the first housing  10  and the second housing  30  are folded or unfolded relative to each other, the movable end  912  of the first synchronous swing arm  91  slides and rotates relative to the first fixed bracket  31 . 
     For example, the rotating end  911  of the first synchronous swing arm  91  includes a first rotating body  9111 , a first rotating shaft  9112 , and a first gear  9113 . The first rotating body  9111  includes a front facet and a back facet that are disposed back to back, and a circumferential side facet connected between the front facet and the back facet. The first gear  9113  is fastened to the circumferential side facet of the first rotating body  9111 . The first rotating shaft  9112  is fastened to the front facet and/or the back facet of the first rotating body  9111 . In embodiments of this application, “A and/or B” includes three cases: “A”, “B”, and “A and B”. In some embodiments, the first rotating shaft  9112  includes two parts, and the two parts are respectively fastened to the front facet and the back facet of the first rotating body  9111 , so that the first synchronous swing arm  91  has improved balance and stability when being rotatably connected to another structure by using the first rotating shaft  9112 . In some other embodiments, the first rotating shaft  9112  includes one part, and the first rotating shaft  9112  is fastened to the front facet or the back facet of the first rotating body  9111 , to lower a requirement for space of the first synchronous swing arm  91 . The first rotating shaft  9112  is configured to be rotatably connected to the main shaft assembly  1 . The first synchronous swing arm  91  may be disposed in one of M-shaped grooves  132  (as shown in  FIG.  17   ) of the main shaft assembly  1 , and the first rotating shaft  9112  is disposed in one recess groove  133  of the M-shaped groove  132 . In this embodiment, the rotating end  911  of the first synchronous swing arm  91  is rotatably connected to the main shaft assembly  1  by using a physical shaft. In some other embodiments, the rotating end  911  of the first synchronous swing arm  91  may alternatively be rotatably connected to the main shaft assembly  1  by using a virtual shaft. This is not strictly limited in this embodiment of this application. 
     For example, the movable end  912  of the first synchronous swing arm  91  includes a third rotating body  9121  and a third rotating shaft  9122 , and the third rotating shaft  9122  is fastened to a front facet and/or a back facet of the third rotating body  9121 . The movable end  912  of the first synchronous swing arm  91  may be disposed in the third sliding slot  316  of the first fixed bracket  31 , and the third rotating shaft  9122  may be disposed in the guiding space  3161  of the third sliding slot  316 . The movable end  912  of the first synchronous swing arm  91  can slide and rotate relative to the first fixed bracket  31 . 
     In this embodiment, the guiding space  3161  of the third sliding slot  316  cooperates with the first rotating shaft  9112  of the first synchronous swing arm  91 , so that the movable end  912  of the first synchronous swing arm  91  can be guided in a sliding direction of the third sliding slot  316 . In this way, a relative movement action between the first synchronous swing arm  91  and the first fixed bracket  31  is easier to implement and control precision is higher. 
     As shown in  FIG.  18    and  FIG.  19   , for example, the second synchronous swing arm  92  includes a rotating end  921  and a movable end  922 , the rotating end  921  of the second synchronous swing arm  92  is rotatably connected to the main shaft assembly  1 , the rotating end  921  of the second synchronous swing arm  92  is engaged with the rotating end  911  of the first synchronous swing arm  91 , and the movable end  922  of the second synchronous swing arm  92  is movably connected to the second fixed bracket  32 . When the first housing  10  and the second housing  30  are folded or unfolded relative to each other, the movable end  922  of the second synchronous swing arm  92  slides and rotates relative to the second fixed bracket  32 . 
     In this embodiment, the rotating end  911  of the first synchronous swing arm  91  and the rotating end  921  of the second synchronous swing arm  92  are engaged with each other, and both the rotating end  911  of the first synchronous swing arm  91  and the rotating end  921  of the second synchronous swing arm  92  are rotatably connected to the main shaft assembly  1 , the movable end  912  of the first synchronous swing arm  91  is movably connected to the first fixed bracket  31 , and the movable end  922  of the second synchronous swing arm  92  is movably connected to the second fixed bracket  32 . Therefore, when the first fixed bracket  31  and the second fixed bracket  32  are unfolded or folded relative to each other, the first synchronous swing arm  91  and the second synchronous swing arm  92  can control rotation angles of the first fixed bracket  31  and the second fixed bracket  32  to be consistent relative to the main shaft assembly  1 , so that rotation actions of the first fixed bracket  31  and the second fixed bracket  32  are synchronous and consistent. Symmetry of folding actions and unfolding actions of the rotating mechanism  20  is high. This helps improve user experience. 
     The first synchronous swing arm  91  is rotatably connected to the main shaft assembly  1 , and slidably and rotatably connected to the first fixed bracket  31 , so that a link-slider structure is formed. The second synchronous swing arm  92  is rotatably connected to the main shaft assembly  1 , and slidably and rotatably connected to the second fixed bracket  32 , so that a link-slider structure is formed. The two link-slider structures that are engaged with each other can effectively control the rotation actions of the first housing  10  and the second housing  30  to be synchronous and consistent. 
     In some embodiments, as shown in  FIG.  19   , the rotating end  921  of the second synchronous swing arm  92  includes a second rotating body  9211 , a second rotating shaft  9212 , and a second gear  9213 . The second rotating shaft  9212  is fastened to a front facet and/or a back facet of the second rotating body  9211 , and the second gear  9213  is fastened to a circumferential side facet of the second rotating body  9211 . The rotating end  921  of the second synchronous swing arm  92  may be disposed in one of the M-shaped grooves  132  (as shown in  FIG.  17   ) of the main shaft assembly  1 , and the second rotating shaft  9212  is disposed in the other recess groove  133  of the M-shaped groove  132 . The second rotating shaft  9212  is rotatably connected to the main shaft assembly  1 , and the second gear  9213  is engaged with the first gear  9113 . 
     In this embodiment, the rotating end  911  of the first synchronous swing arm  91  and the rotating end  921  of the second synchronous swing arm  92  are directly engaged with each other by using the first gear  9113  and the second gear  9213 , so that a synchronization assembly jointly formed by the first synchronous swing arm  91  and the second synchronous swing arm  92  has a simple structure, a movement process is easy to control, and accuracy is high. 
     For example, the movable end  922  of the second synchronous swing arm  92  has a fourth rotating shaft  9221 , the second synchronous swing arm  92  is disposed in the fourth sliding slot  326 , and the fourth rotating shaft  9221  is disposed in the guiding space  3261  of the fourth sliding slot  326 . The guiding space  3261  of the fourth sliding slot  326  cooperates with the fourth rotating shaft  9221  of the second synchronous swing arm  92 , so that the movable end  922  of the second synchronous swing arm  92  can be guided in a sliding direction of the fourth sliding slot  326 . In this way, a relative movement action between the second synchronous swing arm  92  and the second fixed bracket  32  is easier to implement and control precision is higher. 
     In some other embodiments, the first synchronous swing arm  91  may alternatively be connected to the first fixed bracket  31  by using a connector, and the second synchronous swing arm  92  may alternatively be connected to the second fixed bracket  32  by using a connector. For example, the rotating mechanism  20  further includes a first connector and a second connector. The first connector is slidably disposed in the guiding space  3161  of the third sliding slot  316 , the first rotating shaft  9112  is rotatably connected to the first connector, the second connector is slidably disposed in the guiding space  3261  of the fourth sliding slot  326 , and the second rotating shaft  9212  is rotatably connected to the second connector. 
     For example, a structure of the second synchronous swing arm  92  may be approximately the same as a structure of the first synchronous swing arm  91 , to reduce material types of the rotating mechanism  20 , and reduce design difficulty and costs of the rotating mechanism  20 . A structure difference between the second synchronous swing arm  92  and the first synchronous swing arm  91  lies in that the first gear  9113  and the second gear  9213  are arranged at different angles, to facilitate engagement of the first gear  9113  and the second gear  9213 . 
       FIG.  27    is a schematic diagram of a structure of the middle connecting assembly  20   b  shown in  FIG.  10    from another angle, and  FIG.  28    is a schematic diagram of an exploded structure of the middle connecting assembly  20   b  shown in  FIG.  27   . 
     In some embodiments, the middle connecting assembly  20   b  of the rotating mechanism  20  includes a third transmission arm  40 , a third fixed bracket  33 , a fourth transmission arm  50 , and a fourth fixed bracket  34 . The third fixed bracket  33  is fastened to the first housing  10 . One end of the third transmission arm  40  is rotatably connected to the main shaft assembly  1 , and the other end of the third transmission arm  40  is slidably connected to the third fixed bracket  33 . The fourth fixed bracket  34  is fastened to the second housing  30 . One end of the fourth transmission arm  50  is rotatably connected to the main shaft assembly  1 , and the other end of the fourth transmission arm  50  is slidably connected to the fourth fixed bracket  34 . 
     In this embodiment, the third transmission arm  40 , the third fixed bracket  33 , the fourth transmission arm  50 , and the fourth fixed bracket  34  are disposed in the rotating mechanism  20  to increase interaction force between the first housing  10  and the second housing  30 , and the rotating mechanism  20 , so that the folding apparatus  100  is easier to fold and unfold. 
     For example, there is a fifth sliding slot  331  on the third fixed bracket  33 , and a middle part of a slot wall of the fifth sliding slot  331  is recessed to form a guiding space  3311  of the fifth sliding slot  331 . The third transmission arm  40  includes a sliding end  401  and a rotating end  402 . The sliding end  401  of the third transmission arm  40  has a third flange  4011 . The sliding end  401  of the third transmission arm  40  is disposed in the fifth sliding slot  331 , and the third flange  4011  is disposed in the guiding space  3311  of the fifth sliding slot  331 . The rotating end  402  of the third transmission arm  40  is arc-shaped and is disposed in one of the arc-shaped grooves  131  of the main shaft assembly  1 . In this case, the third transmission arm  40  is rotatably connected to the main shaft assembly  1  by using a virtual shaft. In some other embodiments, the third transmission arm  40  may alternatively be rotatably connected to the main shaft assembly  1  by using a physical shaft. This is not strictly limited in this embodiment of this application. 
     The rotating end  402  of the third transmission arm  40  includes a limiting bulge and a limiting projection, and the limiting bulge is formed on an inner side of the rotating end  402  and the limiting projection is formed on an end part of the rotating end  402 . The limiting bulge is configured to cooperate with the limiting groove of the main shaft assembly  1 , so that mutual limiting of the third transmission arm  40  and the main shaft assembly  1  is implemented in the axial direction of the main shaft assembly  1 . The limiting projection is configured to cooperate with the projection of the main shaft assembly  1  that has a limiting function, to prevent the third transmission arm  40  from being accidentally detached from the main shaft assembly  1 . 
     For example, a structure of the fourth fixed bracket  34  may be the same as a structure of the third fixed bracket  33 , and a structure of the fourth transmission arm  50  may be the same as a structure of the third transmission arm  40 . Details are not described in this embodiment of this application. 
     In some embodiments, as shown in  FIG.  10   , a rotation center  40 C around which the third transmission arm  40  rotates relative to the main shaft assembly  1  and the rotation center  4 C around which the first transmission arm  4  rotates relative to the main shaft assembly  1  are collinear. A rotation center  50 C around which the fourth transmission arm  50  rotates relative to the main shaft assembly  1  and the rotation center  6 C around which the second transmission arm  6  rotates relative to the main shaft assembly  1  are collinear. 
     In this embodiment, the rotation centers around which the third transmission arm  40  and the first transmission arm  4  rotate relative to the main shaft assembly  1  are collinear, and the third transmission arm  40  is slidably connected to the third fixed bracket  33 , and the rotation centers around which the fourth transmission arm  50  and the second transmission arm  6  rotate relative to the main shaft assembly  1  are collinear, and the fourth transmission arm  50  is slidably connected to the fourth fixed bracket  34 . In this way, movement of the third transmission arm  40  can be synchronized with movement of the first transmission arm  4 , and movement of the fourth transmission arm  50  can be synchronized with movement of the second transmission arm  6 , so that a structure design and a connection relationship of the rotating mechanism  20  can be simplified, and reliability of the rotating structure is improved. In addition, a structure of the third transmission arm  40  may be the same as a structure of the first transmission arm  4 , and a structure of the fourth transmission arm  50  may be the same as a structure of the second transmission arm  6 , to reduce design difficulty of the rotating mechanism  20 . 
       FIG.  29    is a schematic diagram of a partial structure of the rotating mechanism  20  shown in  FIG.  7   . 
     In some embodiments, the first supporting plate  21  is fixedly connected to the sliding end  41  of the first transmission arm  4 , and the second supporting plate  22  is fixedly connected to the sliding end  61  of the second transmission arm  6 . The first shielding plate  23  is located on a side that is of the first transmission arm  4  and that faces away from the first supporting plate  21 , and is fixedly connected to the sliding end  41  of the first transmission arm  4 . The second shielding plate  24  is located on a side that is of the second transmission arm  6  and that faces away from the second supporting plate  22 , and is fixedly connected to the sliding end  61  of the second transmission arm  6 . In other words, both the first supporting plate  21  and the first shielding plate  23  are fastened to the sliding end  41  of the first transmission arm  4 , and are respectively located on two sides of the first transmission arm  4 . Both the second supporting plate  22  and the second shielding plate  24  are fastened to the sliding end  61  of the second transmission arm  6 , and are respectively located on two sides of the second transmission arm  6 . 
     In this embodiment, the first supporting plate  21 , the first shielding plate  23 , and the first transmission arm  4  are assembled into one component, and the second supporting plate  22 , the second shielding plate  24 , and the second transmission arm  6  are assembled into one component. Therefore, the first transmission arm  4  can directly control motion tracks of the first supporting plate  21  and the first shielding plate  23 , and the second transmission arm  6  can directly control motion tracks of the second supporting plate  22  and the second shielding plate  24 . In this way, precision is high in controlling movement processes of the first supporting plate  21 , the second supporting plate  22 , the first shielding plate  23 , and the second shielding plate  24 , and hysteresis is small, to implement accurately extending or retracting when the folding apparatus  100  is rotated, so as to meet a requirement of supporting the flexible display  200  and a self-shielding requirement of the rotating mechanism  20 . 
     For example, both the first supporting plate  21  and the first shielding plate  23  are fastened to first transmission arms  4  of the two end connecting assemblies  20   a , and may further be fastened to the third transmission arm  40  of the middle connecting assembly  20   b , and both the second supporting plate  22  and the second shielding plate  24  are fastened to second transmission arms  6  of the two end connecting assemblies  20   a , and may further be fastened to the fourth transmission arm  50  of the middle connecting assembly  20   b . In this case, the plurality of connecting assemblies (the assemblies  20   a  and the assembly  20   b ) may jointly drive the first supporting plate  21 , the first shielding plate  23 , the second supporting plate  22 , and the second shielding plate  24  to move, so that motion control difficulty is reduced and motion control precision is improved. 
     In some embodiments, sliding ends of a plurality of transmission arms can be locked and fastened to the supporting plate and the shielding plate by using fasteners. The fastener includes but is not limited to a screw, a bolt, a rivet, a dowel pin, and the like. Concave-convex fitting structures may be further disposed between the sliding ends of the plurality of transmission arms and the supporting plate, and between the sliding ends of the plurality of transmission arms and the shielding plate, so that assembly precision and reliability are improved. For example, as shown in  FIG.  24   , there is further a positioning hole  414  on the sliding end  41  of the first transmission arm  4 . As shown in  FIG.  8   , the first supporting plate  21  includes a positioning block  211 . The positioning block  211  of the first supporting plate  21  may be embedded into the positioning hole  414  of the first transmission arm  4 , to implement mutual positioning and limiting between the first supporting plate  21  and the first transmission arm  4 . 
     In some embodiments, as shown in  FIG.  29   , the first supporting plate  21  and/or the first shielding plate  23  further include/includes one or more supporting columns, configured to support the first supporting plate  21  and the first shielding plate  23 , to improve support strength of the first supporting plate  21  and the first shielding plate  23 . The second supporting plate  22  and/or the second shielding plate  24  further include/includes one or more supporting columns  25 , configured to support the second supporting plate  22  and the second shielding plate  24 , to improve support strength of the second supporting plate  22  and the second shielding plate  24 . 
       FIG.  30    is a schematic diagram of a partial structure of the folding apparatus  100  shown in  FIG.  2   . The structure shown in  FIG.  30    includes the first housing  10 , first fixed brackets  31  of the two end connecting assemblies  20   a , and the third fixed bracket  33  of the middle connecting assembly  20   b . 
     In some embodiments, there is a first fixed groove  102  on a side that is of the first housing  10  and that is close to the rotating mechanism  20 , the first housing  10  includes a first positioning plate  103  located in the first fixed groove  102 , the first positioning plate  103  and a groove bottom wall of the first fixed groove  102  are spaced, and the first fixed bracket  31  is located between the first positioning plate  103  and the groove bottom wall of the first fixed groove  102 , and is fixedly connected to the first positioning plate  103 . In this embodiment, because the first fixed bracket  31  and the first housing  10  are fastened to each other, the first housing  10  moves with the first fixed bracket  31 , and the rotating mechanism  20  may control a motion trail of the first housing  10  by controlling a motion trail of the first fixed bracket  31 . 
     In some embodiments, the first housing  10  has a first supporting surface  101 , and the first positioning plate  103  sinks relative to the first supporting surface  101  to form a first accommodating groove  104 . The first accommodating groove  104  can provide an accommodation and movement space for the first supporting plate  21 . A location at which the first accommodating groove  104  is disposed enables a supporting surface of the first supporting plate  21  disposed in the first accommodating groove  104  to be flush with the first supporting surface  101  of the first housing  10 . In this way, the first supporting plate  21  can better support the flexible display  200 . A depth of the first accommodating groove  104  is very shallow, and a supporting backplane with high hardness is disposed on a non-display side of the flexible display  200 . Therefore, when the first supporting plate  21  partially extends out of the first accommodating groove  104 , a part that is of the flexible display  200  and that faces the first accommodating groove  104  does not deform significantly when been pressed by a user. This also ensures reliability of the flexible display  200 . 
     For example, the third fixed bracket  33  is located between the first positioning plate  103  and the groove bottom wall of the first fixed groove  102 , and is fixedly connected to the first positioning plate  103 . A gap  105  is formed between the two first fixed brackets  31  and the third fixed bracket  33 , and the groove bottom wall of the first fixed groove  102 , and the gap  105  is used to provide an accommodation and movement space for the first shielding plate  23 . 
     For example, the first positioning plate  103  may include a plurality of structures spaced from each other, or may be a continuous structure. This is not strictly limited in this application. The first fixed brackets  31  and the third fixed bracket  33  may be locked with the first positioning plate  103  by using fasteners. The fastener may be but is not limited to a structure such as a screw, a bolt, or a rivet. In some other embodiments, another connection structure may be alternatively formed between the first fixed brackets  31  and the third fixed bracket  33 , and the first housing  10 . This is not strictly limited in this application. 
       FIG.  31    is a schematic diagram of a partial structure of the folding apparatus  100  shown in  FIG.  2   . The structure shown in  FIG.  31    includes the second housing  30 , second fixed brackets  32  of the two end connecting assemblies  20   a , and the fourth fixed bracket  34  of the middle connecting assembly  20   b . 
     In some embodiments, there is a second fixed groove  302  on a side that is of the second housing  30  and that is close to the rotating mechanism  20 , the second housing  30  includes a second positioning plate  303  located in the second fixed groove  302 , the second positioning plate  303  and a groove bottom wall of the second fixed groove  302  are spaced, and the second fixed bracket  32  is located between the second positioning plate  303  and the groove bottom wall of the second fixed groove  302 , and is fixedly connected to the second positioning plate  303 . In this embodiment, because the second fixed bracket  32  and the second housing  30  are fastened to each other, the second housing  30  moves with the second fixed bracket  32 , and the rotating mechanism  20  may control a motion trail of the second housing  30  by controlling a motion trail of the second fixed bracket  32 . 
     In some embodiments, the second housing  30  has a second supporting surface  301 , and the second positioning plate  303  sinks relative to the second supporting surface  301  to form a second accommodating groove  304 . The second accommodating groove  304  can provide an accommodation and movement space for the second supporting plate  22 . A location at which the second accommodating groove  304  is disposed enables a supporting surface of the second supporting plate  22  disposed in the second accommodating groove  304  to be flush with the second supporting surface  301  of the second housing  30 . In this way, the second supporting plate  22  can better support the flexible display  200 . A depth of the second accommodating groove  304  is very shallow, and the supporting backplane with high hardness is disposed on the non-display side of the flexible display  200 . Therefore, when the second supporting plate  22  partially extends out of the second accommodating groove  304 , a part that is of the flexible display  200  and that faces the second accommodating groove  304  does not deform significantly when been pressed by a user. This also ensures reliability of the flexible display  200 . 
     For example, the fourth fixed bracket  34  is located between the second positioning plate  303  and the groove bottom wall of the second fixed groove  302 , and is fixedly connected to the second positioning plate  303 . A gap  305  is formed between the two second fixed brackets  32  and the fourth fixed bracket  34 , and the groove bottom wall of the second fixed groove  302 , and the gap  305  is used to provide an accommodation and movement space for the second shielding plate  24 . 
     For example, the second positioning plate  303  may include a plurality of structures spaced from each other, or may be a continuous structure. This is not strictly limited in this application. The second fixed brackets  32  and the fourth fixed bracket  34  may be locked with the second positioning plate  303  by using fasteners. The fastener may be but is not limited to a structure such as a screw, a bolt, or a rivet. In some other embodiments, another connection structure may be alternatively formed between the second fixed brackets  32  and the fourth fixed bracket  34 , and the second housing  30 . This is not strictly limited in this application. 
       FIG.  32    is a schematic diagram of a connection relationship between a partial structure of the end connecting assembly  20   a  and the main shaft assembly  1  shown in  FIG.  8   . 
     One end of the first transmission arm  4  is rotatably connected to the main shaft assembly  1  and the other end of the first transmission arm  4  is movably connected to the first fixed bracket  31 . One end of the first rotating arm  5  is rotatably connected to the main shaft assembly  1  and the other end of the first rotating arm  5  is rotatably connected to the first fixed bracket  31 . One end of the second transmission arm  6  is rotatably connected to the main shaft assembly  1  and the other end of the second transmission arm  6  is movably connected to the second fixed bracket  32 . One end of the second rotating arm  7  is rotatably connected to the main shaft assembly  1  and the other end of the second rotating arm  7  is rotatably connected to the second fixed bracket  32 . When both the first transmission arm  4  and the first rotating arm  5  rotate relative to the main shaft assembly  1 , the first fixed bracket  31  can be pulled back to approach the main shaft assembly  1 , or the first fixed bracket  31  can be pushed out to move away from the main shaft assembly  1 . In this way, the first fixed bracket  31  drives the first housing  10  to implement pull-in and push-out motions. When both the second transmission arm  6  and the second rotating arm  7  rotate relative to the main shaft assembly  1 , the second fixed bracket  32  can be pulled back to approach the main shaft assembly  1 , or the second fixed bracket  32  can be pushed out to move away from the main shaft assembly  1 . In this way, the second fixed bracket  32  drives the second housing  30  to implement pull-in and push-out motions. 
     The following describes a structure of the folding apparatus  100  with reference to a plurality of diagrams of internal structures obtained when the folding apparatus  100  is in the flattened state, the intermediate state, and the closed state. 
       FIG.  33    is a schematic cross-sectional diagram of a structure of a position that is of the first transmission arm  4  and that is corresponding to the folding apparatus  100  shown in  FIG.  2   .  FIG.  34    is a schematic cross-sectional diagram of a structure of a position that is of the first transmission arm  4  and that is corresponding to the folding apparatus  100  shown in  FIG.  4   .  FIG.  35    is a schematic cross-sectional diagram of a structure of a position that is of the first transmission arm  4  and that is corresponding to the folding apparatus  100  shown in  FIG.  6   .  FIG.  33    to  FIG.  35    show position changes of the first transmission arm  4  obtained when the folding apparatus  100  is switched from the flattened state to the closed state. 
     As shown in  FIG.  33   , when the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, the first transmission arm  4  is approximately parallel to the main shaft assembly  1 , the rotating end  42  of the first transmission arm  4  is in a rotate-in position relative to the main shaft assembly  1 , the sliding end  41  of the first transmission arm  4  is in a slide-out position relative to the first fixed bracket  31 , and the first transmission arm  4  is away from the first fixed bracket  31  and the first housing  10 . 
     As shown in  FIG.  34   , when the first housing  10  and the second housing  30  are in the intermediate state, the first transmission arm  4  is inclined relative to the main shaft assembly  1 , the rotating end  42  of the first transmission arm  4  is in a partially rotate-out position/partially rotate-in position relative to the main shaft assembly  1 , the sliding end  41  of the first transmission arm  4  is in a partially slide-in position/partially slide-out position relative to the first fixed bracket  31 , and the first transmission arm  4  gradually approaches the first fixed bracket  31  and the first housing  10 . 
     As shown in  FIG.  35   , when the first housing  10  and the second housing  30  are folded relative to each other to the closed state, the first transmission arm  4  is approximately perpendicular to the main shaft assembly  1 , the rotating end  42  of the first transmission arm  4  is in a rotate-out position relative to the main shaft assembly  1 , the sliding end  41  of the first transmission arm  4  is in a slide-in position relative to the first fixed bracket  31 , and the first transmission arm  4  approaches the first fixed bracket  31  and the first housing  10 . 
       FIG.  36    is a schematic cross-sectional diagram of a structure of a position that is of the first rotating arm  5  and that is corresponding to the folding apparatus  100  shown in  FIG.  2   .  FIG.  37    is a schematic cross-sectional diagram of a structure of a position that is of the first rotating arm  5  and that is corresponding to the folding apparatus  100  shown in  FIG.  4   .  FIG.  38    is a schematic cross-sectional diagram of a structure of a position that is of the first rotating arm  5  and that is corresponding to the folding apparatus  100  shown in  FIG.  6   .  FIG.  36    to  FIG.  38    show position changes of the first rotating arm  5  obtained when the folding apparatus  100  is switched from the flattened state to the closed state. 
     As shown in  FIG.  36   , when the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, one end of the first rotating arm  5  is in a rotate-out position relative to the main shaft assembly  1 , and the other end of the first rotating arm  5  is in a rotate-out position relative to the first fixed bracket  31 . As shown in  FIG.  37   , when the first housing  10  and the second housing  30  are in the intermediate state, one end of the first rotating arm  5  is in a partially rotate-out position/partially rotate-in position relative to the main shaft assembly  1 , and the other end of the first rotating arm  5  is in a partially rotate-out position/partially rotate-in position relative to the first fixed bracket  31 . As shown in  FIG.  38   , when the first housing  10  and the second housing  30  are folded relative to each other to the closed state, one end of the first rotating arm  5  is in a rotate-in position relative to the main shaft assembly  1 , and the other end of the first rotating arm  5  is in a rotate-in position relative to the first fixed bracket  31 . 
     In this embodiment, a position of the first rotating arm  5  and a position of the first transmission arm  4  (refer to  FIG.  33    to  FIG.  35   ) are mutually limited, and the first rotating arm  5  and the first transmission arm  4  jointly function, so that the first housing  10  can be rotated relative to the main shaft assembly  1  by using the flexible display  200  as a neutral surface. 
     For example, it can be learned from  FIG.  36    to  FIG.  38    that a rotation radian stroke of one end of the first rotating arm  5  in the first fixed bracket  31  is less than a rotation radian stroke of the other end of the first rotating arm  5  in the main shaft assembly  1 . In some other embodiments, rotation radian strokes of the two ends of the first rotating arm  5  may alternatively be the same, or a rotation radian stroke of one end of the first rotating arm  5  in the first fixed bracket  31  may be greater than a rotation radian stroke of the other end of the first rotating arm  5  in the main shaft assembly  1 . 
       FIG.  39    is a schematic cross-sectional diagram of a structure of a position that is of the second transmission arm  6  and that is corresponding to the folding apparatus  100  shown in  FIG.  2   .  FIG.  40    is a schematic cross-sectional diagram of a structure of a position that is of the second transmission arm  6  and that is corresponding to the folding apparatus  100  shown in  FIG.  4   .  FIG.  41    is a schematic cross-sectional diagram of a structure of a position that is of the second transmission arm  6  and that is corresponding to the folding apparatus  100  shown in  FIG.  6   .  FIG.  39    to  FIG.  41    show position changes of the second transmission arm  6  obtained when the folding apparatus  100  is switched from the flattened state to the closed state. 
     As shown in  FIG.  39   , when the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, the second transmission arm  6  is approximately parallel to the main shaft assembly  1 , the rotating end  62  of the second transmission arm  6  is in a rotate-in position relative to the main shaft assembly  1 , the sliding end  61  of the second transmission arm  6  is in a slide-out position relative to the second fixed bracket  32 , and the second transmission arm  6  is away from the second fixed bracket  32  and the second housing  30 . 
     As shown in  FIG.  40   , when the first housing  10  and the second housing  30  are in the intermediate state, the second transmission arm  6  is inclined relative to the main shaft assembly  1 , the rotating end  62  of the second transmission arm  6  is in a partially rotate-out position/partially rotate-in position relative to the main shaft assembly  1 , the sliding end  61  of the second transmission arm  6  is in a partially slide-in position/partially slide-out position relative to the second fixed bracket  32 , and the second transmission arm  6  gradually approaches the second fixed bracket  32  and the second housing  30 . 
     As shown in  FIG.  41   , when the first housing  10  and the second housing  30  are folded relative to each other to the closed state, the second transmission arm  6  is approximately perpendicular to the main shaft assembly  1 , the rotating end  62  of the second transmission arm  6  is in a rotate-out position relative to the main shaft assembly  1 , the sliding end  61  of the second transmission arm  6  is in a slide-in position relative to the second fixed bracket  32 , and the second transmission arm  6  approaches the second fixed bracket  32  and the second housing  30 . 
       FIG.  42    is a schematic cross-sectional diagram of a structure of a position that is of the second rotating arm  7  and that is corresponding to the folding apparatus  100  shown in  FIG.  2   .  FIG.  43    is a schematic cross-sectional diagram of a structure of a position that is of the second rotating arm  7  and that is corresponding to the folding apparatus  100  shown in  FIG.  4   .  FIG.  44    is a schematic cross-sectional diagram of a structure of a position that is of the second rotating arm  7  and that is corresponding to the folding apparatus  100  shown in  FIG.  6   .  FIG.  42    to  FIG.  44    show position changes of the second rotating arm  7  obtained when the folding apparatus  100  is switched from the flattened state to the closed state. 
     As shown in  FIG.  42   , when the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, one end of the second rotating arm  7  is in a rotate-out position relative to the main shaft assembly  1 , and the other end of the second rotating arm  7  is in a rotate-out position relative to the second fixed bracket  32 . As shown in  FIG.  43   , when the first housing  10  and the second housing  30  are in the intermediate state, one end of the second rotating arm  7  is in a partially rotate-out position/partially rotate-in position relative to the main shaft assembly  1 , and the other end of the second rotating arm  7  is in a partially rotate-out position/partially rotate-in position relative to the second fixed bracket  32 . As shown in  FIG.  44   , when the first housing  10  and the second housing  30  are folded relative to each other to the closed state, one end of the second rotating arm  7  is in a rotate-in position relative to the main shaft assembly  1 , and the other end of the second rotating arm  7  is in a rotate-in position relative to the second fixed bracket  32 . 
     In this embodiment, a position of the second rotating arm  7  and a position of the second transmission arm  6  (refer to  FIG.  39    to  FIG.  41   ) are mutually limited, and the second rotating arm  7  and the second transmission arm  6  jointly function, so that the second housing  30  can be rotated relative to the main shaft assembly  1  by using the flexible display  200  as a neutral surface. 
     For example, it can be learned from  FIG.  42    to  FIG.  44    that a rotation radian stroke of one end of the second rotating arm  7  in the second fixed bracket  32  is less than a rotation radian stroke of the other end of the second rotating arm  7  in the main shaft assembly  1 . In some other embodiments, rotation radian strokes of the two ends of the second rotating arm  7  may alternatively be the same, or a rotation radian stroke of one end of the second rotating arm  7  in the second fixed bracket  32  is greater than a rotation radian stroke of the other end of the second rotating arm  7  in the main shaft assembly  1 . 
     In this embodiment of this application, as shown in  FIG.  33    to  FIG.  44   , the rotating mechanism  20  controls motion tracks of the first fixed bracket  31  and the first housing  10  by using both the first transmission arm  4  and the first rotating arm  5 , and controls motion tracks of the second fixed bracket  32  and the second housing  30  by using both the second transmission arm  6  and the second rotating arm  7 . Therefore, when the first housing  10  and the second housing  30  are folded relative to each other, the rotating mechanism  20  enables the first fixed bracket  31  to drive the first housing  10  to approach the main shaft assembly  1 , and enables the second fixed bracket  32  to drive the second housing  30  to approach the main shaft assembly  1 . When the first housing  10  and the second housing  30  are unfolded relative to each other, the rotating mechanism  20  enables the first fixed bracket  31  to drive the first housing  10  to move away from the main shaft assembly  1 , and enables the second fixed bracket  32  to drive the second housing  30  to move away from the main shaft assembly  1 . In other words, the rotating mechanism  20  can implement pulling-in of the housing when the folding apparatus  100  is switched from the flattened state to the closed state and pushing-out of the housing when the folding apparatus  100  is switched from the closed state to the flattened state, so that the folding apparatus  100  can implement deformation by using the flexible display  200  as a neutral surface when being unfolded or folded. In this way, a risk that the flexible display  200  is stretched or squeezed is reduced, to protect the flexible display  200  and improve reliability of the flexible display  200 , so that the flexible display  200  and the electronic device  1000  have long service lives. 
     In addition, when the first housing  10  and the second housing  30  are folded relative to each other to the closed state by using the rotating mechanism  20 , the first housing  10  and the second housing  30  can be completely closed, and there is no gap between the first housing  10  and the second housing  30  or a gap between the first housing  10  and the second housing  30  is small. Therefore, appearance integrity of the folding apparatus  100  is implemented, and self-shielding in appearance is implemented. Appearance integrity of the electronic device  1000  to which the folding apparatus  100  is applied is implemented, so that product reliability and user experience are improved. 
     In addition, the first transmission arm  4  is rotatably connected to the main shaft assembly  1  and slidably connected to the first fixed bracket  31  to form a link-slider structure, and the first rotating arm  5  is rotatably connected to the main shaft assembly  1  and rotatably connected to the first fixed bracket  31  to form a link structure. The second transmission arm  6  is rotatably connected to the main shaft assembly  1  and is slidably connected to the second fixed bracket  32  to form a link-slider structure. The second rotating arm  7  is rotatably connected to the main shaft assembly  1  and rotatably connected to the second fixed bracket  32  to form a link structure. In the rotating mechanism  20 , the housing is connected to the main shaft assembly  1  by using the link-slider structure and the link structure. A quantity of components of the rotating mechanism  20  is small, a cooperation relationship and a cooperation position are simple, and the components are easy to manufacture and assemble. This facilitates mass production. In addition, because the main shaft assembly  1  is associated with the first fixed bracket  31  by using the first transmission arm  4  and the first rotating arm  5 , and the main shaft assembly  1  is associated with the second fixed bracket  32  by using the second transmission arm  6  and the second rotating arm  7 , the rotating mechanism  20  has a better mechanism stretching-resistance capability and mechanism squeezing-resistance capability. 
     As shown in  FIG.  35   , when the first housing  10  and the second housing  30  are folded relative to each other to the closed state, the main inner shaft  15  of the main shaft assembly  1  is located between the main outer shaft  14  and each of the first fixed bracket  31  and the second fixed bracket  32 . As shown in  FIG.  35   ,  FIG.  38   ,  FIG.  41    and  FIG.  44   , the rotation center around which the first transmission arm  4  rotates relative to the main shaft assembly  1  is close to the main inner shaft  15  and away from the main outer shaft  14 , and the rotation center around which the first rotating arm  5  rotates relative to the main shaft assembly  1  is close to the main outer shaft  14  and away from the main inner shaft  15 . The rotation center around which the second transmission arm  6  rotates relative to the main shaft assembly  1  is close to the main inner shaft  15  and away from the main outer shaft  14 , and the rotation center around which the second rotating arm  7  rotates relative to the main shaft assembly  1  is close to the main outer shaft  14  and away from the main inner shaft  15 . 
     In this embodiment, locations of the rotation center around which the first transmission arm  4  rotates relative to the main shaft assembly  1 , the rotation center around which the first rotating arm  5  rotates relative to the main shaft assembly  1 , the rotation center around which the second transmission arm  6  rotates relative to the main shaft assembly  1 , and the rotation center around which the second rotating arm  7  rotates relative to the main shaft assembly  1  are set, so that the rotating mechanism  20  can more easily implement pulling-in of the housing when the folding apparatus  100  is switched from the flattened state to the closed state and pushing-out of the housing when the folding apparatus  100  is switched from the closed state to the flattened state. 
     As shown in  FIG.  33   , when the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, the first supporting plate  21  is flush with the second supporting plate  22 , the first supporting plate  21  is laid between the first fixed bracket  31  and the main shaft assembly  1 , and the second supporting plate  22  is laid between the second fixed bracket  32  and the main shaft assembly  1 . The first supporting plate  21 , the main shaft assembly  1 , and the second supporting plate  22  can jointly form a complete planar support for the bending part  2002  of the flexible display  200 . As shown in  FIG.  35   , when the first housing  10  and the second housing  30  are folded relative to each other to the closed state, the first supporting plate  21  is stacked on a side that is of the first fixed bracket  31  and that is away from the second fixed bracket  32 , and the second supporting plate  22  is stacked on a side that is of the second fixed bracket  32  and that is away from the first fixed bracket  31 . The first supporting plate  21  and the second supporting plate  22  can slide and be accommodated relative to the first housing  10  and the second housing  30  respectively, so that the main shaft assembly  1  is exposed to form complete support for the bending part  2002  of the flexible display  200 . In other words, when the folding apparatus  100  is in the flattened state or the closed state, the rotating mechanism  20  can completely support the bending part  2002  of the flexible display  200 , thereby helping protect the flexible display  200  and improving user experience. 
     As shown in  FIG.  33   , when the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, the first shielding plate  23  is flush with the second shielding plate  24 , the first shielding plate  23  is laid between the first fixed bracket  31  and the main shaft assembly  1 , and can shield a gap between the first fixed bracket  31  and the main shaft assembly  1 , and the second shielding plate  24  is laid between the second fixed bracket  32  and the main shaft assembly  1 , and can shield a gap between the second fixed bracket  32  and the main shaft assembly  1 . Therefore, the folding apparatus  100  can implement self-shielding. In this way, appearance integrity is improved, a risk that dust, sundries, and the like enter the rotating mechanism  20  from outside can also be lowered, to ensure reliability of the folding apparatus  100 . As shown in  FIG.  35   , when the first housing  10  and the second housing  30  are folded relative to each other to the closed state, the first shielding plate  23  can be accommodated between the first fixed bracket  31  and the first housing  10 , and the second shielding plate  24  can be accommodated between the second fixed bracket  32  and the second housing  30 , so that avoidance is achieved. In this way, the folding apparatus  100  can be smoothly folded to the closed form, and mechanism reliability is high. 
     As shown in  FIG.  33    and  FIG.  39   , the first supporting plate  21  and the first shielding plate  23  are fastened to the sliding end  41  of the first transmission arm  4 , and the first supporting plate  21  and the first shielding plate  23  move with the sliding end  41  of the first transmission arm  4 , and the second supporting plate  22  and the second shielding plate  24  are fastened to the sliding end  61  of the second transmission arm  6 , and the second supporting plate  22  and the second shielding plate  24  move with the sliding end  61  of the second transmission arm  6 . Therefore, when the folding apparatus  100  is switched from the closed state to the flattened state or when the folding apparatus  100  is switched from the flattened state to the closed state, the first supporting plate  21  and the second supporting plate  22  gradually approach the main shaft assembly  1  or move away from the main shaft assembly  1 , so that the folding apparatus  100  can completely support the flexible display  200  in various forms. In this way, reliability of the flexible display  200  and the electronic device  1000  is improved and service lives of the flexible display  200  and the electronic device  1000  are increased. In addition, when the folding apparatus  100  is switched from the closed state to the flattened state or when the folding apparatus  100  is switched from the flattened state to the closed state, the first shielding plate  23  and the second shielding plate  24  gradually approach the main shaft assembly  1  or move away from the main shaft assembly  1 , so that the folding apparatus  100  in the various forms can adapt to forms of the rotating mechanism  20 , to implement self-shielding. In this way, mechanism reliability is high. 
     Moreover, because both the first supporting plate  21  and the first shielding plate  23  are fastened to the sliding end  41  of the first transmission arm  4 , and both the second supporting plate  22  and the second shielding plate  24  are fastened to the sliding end  61  of the second transmission arm  6 , the first transmission arm  4  and the second transmission arm  6  not only control rotation actions of the first housing  10  and the second housing  30 , but also control extending or retracting of the first supporting plate  21 , the first shielding plate  23 , the second supporting plate  22 , and the second shielding plate  24 . Therefore, the rotating mechanism  20  is highly integrated, an overall connection relationship is simple, and mechanism reliability is high. 
       FIG.  45    is a schematic cross-sectional diagram of a structure of positions that are of the first synchronous swing arm  91  and the second synchronous swing arm  92  and that are corresponding to the folding apparatus  100  shown in  FIG.  2   .  FIG.  46    is a schematic cross-sectional diagram of a structure of positions that are of the first synchronous swing arm  91  and the second synchronous swing arm  92  and that are corresponding to the folding apparatus  100  shown in  FIG.  4   .  FIG.  47    is a schematic cross-sectional diagram of a structure of positions that are of the first synchronous swing arm  91  and the second synchronous swing arm  92  and that are corresponding to the folding apparatus  100  shown in  FIG.  6   .  FIG.  45    to  FIG.  47    show position changes of the first synchronous swing arm  91  and the second synchronous swing arm  92  obtained when the folding apparatus  100  is switched from the flattened state to the closed state. 
     As shown in  FIG.  45   , when the first housing  10  and the second housing  30  are unfolded relative to each other to the flattened state, the first synchronous swing arm  91  and the second synchronous swing arm  92  are in a flattened state, the first synchronous swing arm  91  is in an extend-out position relative to the first fixed bracket  31 , the first synchronous swing arm  91  is away from the first fixed bracket  31  and the first housing  10 , the second synchronous swing arm  92  is in an extend-out position relative to the second fixed bracket  32 , and the second synchronous swing arm  92  is away from the second fixed bracket  32  and the second housing  30 . 
     As shown in  FIG.  46   , when the first housing  10  and the second housing  30  are in the intermediate state, the first synchronous swing arm  91  and the second synchronous swing arm  92  are in an intermediate state, and an included angle is formed between the first synchronous swing arm  91  and the second synchronous swing arm  92 . The first synchronous swing arm  91  is in a partially extend-out position/partially retracted position relative to the first fixed bracket  31 , and the second synchronous swing arm  92  is in a partially extend-out position/partially retracted position relative to the second fixed bracket  32 . 
     As shown in  FIG.  47   , when the first housing  10  and the second housing  30  are folded relative to each other to the closed state, the first synchronous swing arm  91  and the second synchronous swing arm  92  are in a folded state, the first synchronous swing arm  91  is in a retracted position relative to the first fixed bracket  31 , the first synchronous swing arm  91  is close to the first fixed bracket  31  and the first housing  10 , the second synchronous swing arm  92  is in a retracted position relative to the second fixed bracket  32 , and the second synchronous swing arm  92  is close to the second fixed bracket  32  and the second housing  30 . 
     In this embodiment, the rotating end  911  of the first synchronous swing arm  91  and the rotating end  921  of the second synchronous swing arm  92  are engaged with each other, and both the rotating end  911  of the first synchronous swing arm  91  and the rotating end  921  of the second synchronous swing arm  92  are rotatably connected to the main shaft assembly  1 , the movable end  912  of the first synchronous swing arm  91  is movably connected to the first fixed bracket  31 , and the movable end  922  of the second synchronous swing arm  92  is movably connected to the second fixed bracket  32 . Therefore, when the first housing  10  and the second housing  30  are unfolded or folded relative to each other, the first synchronous swing arm  91  and the second synchronous swing arm  92  can control rotation angles of the first fixed bracket  31  and the second fixed bracket  32  to be consistent relative to the main shaft assembly  1 , so that rotation actions of the first housing  10  and the second housing  30  are synchronous and consistent. Symmetry of folding actions and unfolding actions of the folding apparatus  100  is high. This helps improve user experience. 
     The first synchronous swing arm  91  is rotatably connected to the main shaft assembly  1 , and slidably and rotatably connected to the first fixed bracket  31 , so that a link-slider structure is formed. The second synchronous swing arm  92  is rotatably connected to the main shaft assembly  1 , and slidably and rotatably connected to the second fixed bracket  32 , so that a link-slider structure is formed. The two link-slider structures that are engaged with each other can effectively control the rotation actions of the first housing  10  and the second housing  30  to be synchronous and consistent. 
     According to embodiments of this application, the folding apparatus  100  can implement pulling-in of the housing when the folding apparatus  100  is switched from the flattened state to the closed state and pushing-out of the housing when the folding apparatus  100  is switched from the closed state to the flattened state, to implement deformation by using the flexible display  200  as a neutral surface when being unfolded or folded. In this way, a risk that the flexible display  200  is stretched or squeezed is reduced, to protect the flexible display  200  and improve reliability of the flexible display  200 , so that the flexible display  200  and the electronic device  1000  have long service lives. 
     The foregoing descriptions are merely specific embodiments of this application, but are not intended to limit the protection scope of this application. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in this application, for example, reducing or adding a mechanical part, or changing a shape of a mechanical part, shall fall within the protection scope of this application. In a case that no conflict occurs, embodiments in this application and features in embodiments may be mutually combined. Therefore, the protection scope of this application shall be subject to the protection scope of the claims.