Focusing device and projection device

Abstract

A focusing device (100), characterized in that it comprises: a focus lens (110) comprising a focus lens tube (111) and a lens body (112); wherein the lens body (112) has an optical axis (AA) and the lens body (112) is movably arranged in the focus lens tube (111) along the extension direction of the optical axis (AA); a focusing element (120) which is rotatably arranged about the optical axis (AA) on the focusing lens tube (111) and engages with the objective body (112); wherein the focusing element (120) can move the objective body (112) along the extension direction of the optical axis (AA) when rotated and the objective body (112) does not rotate relative to the focusing lens tube (111); a magnetic part (130); and a magnetic sensor (140) for detecting the magnetic signal of the magnetic part (130); where one of cases 1 and 2 is fulfilled, In case 1: one of the magnetic part (130) and the magnetic sensor (140) is fixedly arranged relative to the focusing element (120), and the other of the magnetic part (130) and the magnetic sensor (140) is fixedly arranged relative to the focusing lens tube (111); and In case 2: one of the magnetic part (130) and the magnetic sensor (140) is fixedly arranged relative to the lens body (112), and the other of the magnetic part (130) and the magnetic sensor (140) is fixedly arranged relative to the focus lens tube (111).

Description

Technical field

[0001] The present application concerns the field of projection technology and relates in particular to a focusing device and a projection device. State of the art

[0002] The operating principle of a projector is to shine light onto an image display element to create an image, which is then projected through a lens. Different focal lengths are required when a projector projects images of varying sizes. An incorrect focal length will result in a blurry image.

[0003] In related techniques, a projection lens comprises a lens tube and a retractable objective lens within the lens tube. The lens tube and the objective lens are rotatably connected. When focusing is required, the objective lens can be simultaneously rotated and moved axially by driving a relative rotation between the objective lens and the lens tube to achieve focus.

[0004] However, the relative rotation between the lens and the lens tube leads to accelerated wear and reduces the lifespan. Content of the present application

[0005] The embodiments of the present application provide a focusing device and a projection device. The lens body does not rotate during extension and retraction, resulting in relatively low wear between the lens body and the focusing lens tube and a relatively long service life.

[0006] In a first aspect, one embodiment of the present application provides a focusing device. The focusing device comprises: a focusing lens comprising a focusing lens tube and a lens body; wherein the lens body has an optical axis and the lens body is movably arranged in the focusing lens tube along the extension direction of the optical axis; a focusing element rotatably arranged about the optical axis on the focusing lens tube and engaged with the lens body; wherein, when rotated, the focusing element can move the lens body along the extension direction of the optical axis and the lens body does not rotate relative to the focusing lens tube; a magnetic part; and a magnetic sensor used to detect the magnetic signal of the magnetic part; wherein one of the magnetic part and the magnetic sensor is fixedly arranged relative to the focusing element, and the other of the magnetic part and the magnetic sensor is fixedly arranged relative to the focusing lens tube.

[0007] In a second aspect, one embodiment of the present application provides a focusing device. The focusing device comprises: a focusing lens comprising a focusing lens tube and a lens body; wherein the lens body has an optical axis and the lens body is movably arranged in the focusing lens tube along the extension direction of the optical axis; a focusing element rotatably arranged about the optical axis on the focusing lens tube and engaged with the lens body; wherein, when rotated, the focusing element can move the lens body along the extension direction of the optical axis and the lens body does not rotate relative to the focusing lens tube; a magnetic part; and a magnetic sensor used to detect the magnetic signal of the magnetic part; wherein one of the magnetic part and the magnetic sensor is fixedly arranged relative to the lens body, and the other of the magnetic part and the magnetic sensor is fixedly arranged relative to the focusing lens tube.

[0008] In a third aspect, an embodiment of the present application provides a projection device. The projection device comprises a focusing device and an optical component. The lens body is arranged on a light-exit side of the optical component.

[0009] Advantageous effect: When focusing the focusing device according to the embodiments of the present application, the objective body does not rotate relative to the focusing lens tube, resulting in relatively low wear between the objective body and the focusing lens tube and a relatively long service life. The gap between the objective body and the focusing lens tube can be smaller, which largely prevents the ingress of dust and liquid into the interior and improves dust and moisture protection. Furthermore, the focusing device is more stable during transport or movement, and focus shifts due to vibrations occur less frequently. Brief description of the drawing

[0010] To clarify the technical solution in the embodiments of the present application, the drawings required in these embodiments are briefly presented below. It is evident that the drawings shown in the following description represent only some embodiments of the present application. A person skilled in the art can obtain other drawings based on these, provided that no inventive step is involved. Fig. Figure 1 is a schematic structure diagram of a focusing device according to some embodiments of the present application. Fig. Figure 2 is a schematic structure diagram of a focusing device according to some other embodiments of the present application. Fig. Figure 3 is a schematic structure diagram of a focusing device according to some further embodiments of the present application. Fig. Figure 4 is a schematic structure diagram of a focusing device according to some further embodiments of the present application. Fig. Figure 5 is a block diagram of a focusing device according to some embodiments of the present application. Fig. Figure 6 is a schematic structure diagram of a projection device according to some embodiments of the present application. Detailed description of the embodiments

[0011] The technical solutions in the embodiments of the present application are described clearly and completely below with reference to the drawings in those embodiments. Obviously, the described embodiments represent only a subset of the embodiments of the present application and not all of them. All other embodiments that a person skilled in the art in this field obtains based on the embodiments of the present application, without inventive step, fall within the scope of protection of the present application.

[0012] It should be noted that all directional terms in the embodiments of the present application (such as above, below, left, right, front, back, etc.) serve only to explain the relative positional relationships, states of motion, etc., between the components in a specific position (as shown in the drawings). If this specific position changes, this directional term changes accordingly.

[0013] Furthermore, descriptions such as "first", "second", etc., in this application serve only descriptive purposes and are not to be understood as having a relative meaning or implicitly indicating the number of technical features specified. Therefore, features marked "first", "second", etc., may explicitly or implicitly include at least one such feature. In the description of this application, "several" means at least two, for example, two, three, etc., unless expressly defined otherwise.

[0014] In this application, unless expressly specified and defined otherwise, terms such as "connect", "fasten", etc., are to be understood broadly. For example, "fasten" may refer to a permanent connection, a detachable connection, or a single-piece part; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection via an intermediate medium; it may refer to the connection within two elements or the interaction relationship between two elements, unless expressly defined otherwise. For a person skilled in the art, the specific meaning of the above terms in this application can be understood depending on the specific situation.

[0015] Furthermore, the technical solutions of the various embodiments of the present application can be combined, but this must be done on the basis that a person skilled in the art can implement them. If the combination of technical solutions leads to contradictions or is not feasible, it should be assumed that such a combination of technical solutions does not exist and is not within the scope of protection of the present application.

[0016] As in Fig. As shown in Figures 1-4, a first aspect of the embodiments of the present application provides a focusing device 100. The focusing device 100 comprises a focusing lens 110, a focusing element 120, a magnetic part 130, and a magnetic sensor 140.

[0017] The focus lens 110 comprises a focus lens tube 111 and a lens body 112. The lens body 112 has an optical axis AA, which is an axis passing through the center of the lens body 112. The lens body 112 is movably arranged within the focus lens tube 111 along the direction of extension of the optical axis AA. Optionally, the focus lens tube 111 is mounted externally around the lens body 112, and the lens body 112 is inserted axially displaceably into the focus lens tube 111 to allow the lens body 112 to move relative to the focus lens tube 111 along the direction of extension of the optical axis AA. An optical lens group is installed within the lens body 112. The focus of the projected image can be adjusted by focusing the focus lens 110.

[0018] The focusing element 120 is rotatably arranged about the optical axis AA on the focusing lens tube 111. The focusing element 120 can, for example, be ring-shaped, allowing it to fit closely to the focusing lens tube 111 and require little space. The rotation angle of the focusing element 120 can be, for example, 40°–120°.

[0019] The focusing element 120 interacts with the lens body 112 via a transmission mechanism. When the focusing element 120 rotates, it can move the lens body 112 along the optical axis AA. It should be noted that in these embodiments, the rotation of the focusing element 120 is converted into a linear movement of the lens body 112, so that the lens body 112 does not rotate relative to the focusing lens tube 111.

[0020] In these embodiments of the present application, when focusing the focusing device 100, the lens body 112 does not rotate relative to the focus lens tube 111. This results in relatively low wear between the lens body 112 and the focus lens tube 111, a relatively longer service life, and quieter operation. The gap between the lens body 112 and the focus lens tube 111 can be smaller, largely preventing the ingress of dust and liquid into the interior, improving dust and moisture protection, and reducing the deviation of the optical axis AA when moving the lens body 112, leading to higher focus accuracy. Furthermore, the focusing device 100 is more stable during transport or movement and less susceptible to focus shifts due to vibrations.

[0021] Furthermore, the lenses in the lens tube are difficult to manufacture in a perfectly round shape; therefore, a rotation of the objective body 112 relative to the focusing lens tube 111 would lead to changes in the optical effect, which could impair the projection quality. The focusing device 100 of this embodiment, however, provides a stable optical effect.

[0022] As in Fig. As shown in Figures 1-4, in some embodiments a spiral groove 120a is arranged on the focusing element 120. The spiral groove 120a has an axis, extends spirally around this axis, and the axis of the spiral groove 120a coincides with the optical axis AA. The focusing device 100 also includes a transmission element 180, which is connected to the lens body 112 and is slidably arranged in the spiral groove 120a. The spiral groove 120a has an expansion tendency in the direction of rotation around the optical axis AA and an expansion tendency along the direction of extension of the optical axis AA. That is, the expansion direction of the spiral groove 120a has a component along the optical axis AA. Therefore, when the focusing element 120 rotates, the wall of the spiral groove 120a pushes the transmission element 180 along the extension direction of the optical axis AA, thereby converting the rotation of the focusing element 120 into a linear movement of the lens body 112.It should be noted that the spiral groove 120a does not necessarily have to complete a full rotation around the axis; for example, the spiral groove 120a can extend over one-fifth of a rotation around the axis. The specific length of the spiral groove 120a can be determined according to actual requirements and is not limited here.

[0023] Optionally, the transmission element 180 can be located inside the spiral groove 120a or be flush with it (that is, the transmission element 180 can be flush with an opening end or circumferential surface of the spiral groove 120a) to prevent the transmission element 180 from protruding beyond the spiral groove 120a and causing friction with other parts.

[0024] In other embodiments, the focusing element 120 and the lens body 112 can interact via a threaded connection to convert the rotation of the focusing element 120 into a linear movement of the lens body 112. For example, the inner wall of the focusing element 120 can have an internal thread and the outer wall of the lens body 112 an external thread. The internal thread of the focusing element 120 engages with the external thread of the lens body 112. When the focusing element 120 rotates, it can move the lens body 112. Of course, the transmission connection between the focusing element 120 and the lens body 112 can be implemented in other conventional ways, which are not limited here.

[0025] As in Fig. As shown in Figures 1-4, the focusing device 100 in some embodiments also comprises a magnetic part 130 and a magnetic sensor 140. The magnetic part 130 generates a magnetic field, and the magnetic sensor 140 serves to detect the magnetic signal of the magnetic part 130.

[0026] According to the principle of distance attenuation of the magnetic field, the magnetic sensor 140 receives different magnetic signals B when the relative position between the magnetic part 130 and the magnetic sensor 140 changes. The magnetic sensor 140 serves to determine the relative position of the magnetic part 130 based on the strength of the received magnetic signal B.

[0027] The focusing device 100 has a movable part and a stationary part. During focusing, the movable part moves relative to the stationary part. By attaching one magnetic part 130 and one magnetic sensor 140 to the movable part and the other magnetic part 130 and magnetic sensor 140 to the stationary part, a relative displacement between the magnetic part 130 and the magnetic sensor 140 can be generated. Different distances between the magnetic part 130 and the magnetic sensor 140 result in different magnetic signals from the magnetic part 130 detected by the magnetic sensor 140. By detecting the magnetic signal from the magnetic part 130, the relative positional relationship between the movable part and the stationary part can be determined, thus achieving focus.

[0028] Specifically, in the actual focusing process, the distance d between the focusing lens tube 111 and the projection plane must first be determined. An imaging relationship exists between this distance d and the position t of the lens body 112. This relationship is related to the lens group structure of the focusing lens 110 and can be determined by measurement or theoretical calculation. That is, the imaging relationship between the distance d and the position t of the lens body 112 can be referred to as the first imaging relationship. Using this first imaging relationship, the position t of the lens body 112 that corresponds to the sharpest projection can be determined when the distance between the focusing lens tube 111 and the projection plane is d.

[0029] The position of the lens body 112 is also related to the magnetic signal B detected by the magnetic sensor 140, which can likewise be determined by practical measurement or theoretical calculation. That is, the relationship between the position of the lens body 112 and the magnetic signal B detected by the magnetic sensor 140 can be called the second relationship. Therefore, there is also a relationship between the distance d from the focusing lens tube 111 to the projection plane and the magnetic signal B detected by the magnetic sensor 140. That is, the relationship between the distance d and the magnetic signal B can be called the third relationship. The third relationship can be determined based on the first and second relationships.

[0030] The related technique uses optocoupler detection technology to determine the rotation angle of the focus ring and derive the current position of the lens from it. However, the position data can only be read at the optocoupler's location, and the lens's position cannot be captured in real time.

[0031] In the embodiments of the present application, no optocoupler is required, and the lens body 112 does not need to be moved to the optocoupler. By moving the lens to the magnetic signal B required for the magnetic sensor 140, the focusing process can be completed, thus reducing the time required for the focusing process. Furthermore, in the embodiments, the arrangement of a single magnetic part 130 enables the magnetic sensor 140 to determine the real-time position of the lens body 112 by detecting the signal from this single magnetic part 130. This simplifies the computational complexity, reduces the volume of the magnetic part 130, and lowers development costs.

[0032] In some embodiments, one of the magnetic part 130 and the magnetic sensor 140 is fixedly attached relative to the focusing element 120, and the other of the magnetic part 130 and the magnetic sensor 140 is fixedly attached relative to the focusing lens tube 111. This means that if the magnetic part 130 is fixedly attached relative to the focusing element 120 and the magnetic sensor 140 is fixedly attached relative to the focusing lens tube 111, the connection between the magnetic part 130 and the focusing element 120 can be direct or indirect, and the connection between the magnetic sensor 140 and the focusing lens tube 111 can be direct or indirect.If the magnetic part 130 is fixed relative to the focusing lens tube 111 and the magnetic sensor 140 is fixed relative to the focusing element 120, the connection between the magnetic part 130 and the focusing lens tube 111 can be direct or indirect, and the connection between the magnetic sensor 140 and the focusing element 120 can be direct or indirect.

[0033] In general, the movement amplitude of the focusing element 120 relative to the focusing lens tube 111 is relatively large compared to the linear movement amplitude of the lens body 112, which reduces the requirements for the sensitivity of the magnetic sensor 140, the precision of the lens components, and the precision of the motor. Furthermore, since the movement amplitude of the magnetic part 130 relative to the magnetic sensor 140 is relatively large, the detection of the magnetic field change of the magnetic part 130 by the magnetic sensor 140 is more accurate, which can increase the focusing precision.

[0034] In some embodiments, one of the magnetic part 130 and the magnetic sensor 140 is fixedly attached relative to the lens body 112, and the other of the magnetic part 130 and the magnetic sensor 140 is fixedly attached relative to the focusing lens tube 111. This means that if the magnetic part 130 is fixedly attached relative to the lens body 112 and the magnetic sensor 140 is fixedly attached relative to the focusing lens tube 111, the connection between the magnetic part 130 and the lens body 112 can be direct or indirect, and the connection between the magnetic sensor 140 and the focusing lens tube 111 can be direct or indirect.If the magnetic part 130 is fixed relative to the focus lens tube 111 and the magnetic sensor 140 is fixed relative to the lens body 112, the connection between the magnetic part 130 and the focus lens tube 111 can be direct or indirect, and the connection between the magnetic sensor 140 and the lens body 112 can be direct or indirect.

[0035] As in Fig. 1 and Fig. As shown in Figure 2, in some embodiments one of the magnetic part 130 and the magnetic sensor 140 is attached to the focusing element 120, and the other of the magnetic part 130 and the magnetic sensor 140 is attached to the focusing lens tube 111. When the focusing element 120 rotates, the magnetic part 130 rotates relative to the magnetic sensor 140 about the optical axis AA. That is, the magnetic part 130 is attached to the focusing element 120 and the magnetic sensor 140 is attached to the focusing lens tube 111, or the magnetic sensor 140 is attached to the focusing element 120 and the magnetic part 130 is attached to the focusing lens tube 111. For example, the magnetic part 130 can be attached to the focusing element 120 by gluing, threaded connection, snap connection, press connection, etc., and the magnetic sensor 140 can be attached to the focusing lens tube 111 by gluing, threaded connection, snap connection, press connection, etc.

[0036] The magnetic sensor 140 detects the rotation distance of the lens body 112 in real time via the change in the magnetic field of the magnetic part 130 in order to quickly and accurately obtain the real-time position of the element 120 to be focused.

[0037] In comparison to the transmission element 180, the dimensions of the focusing element 120 and the focusing lens tube 111 are relatively larger, providing sufficient space for the arrangement of the magnetic part 130 and the magnetic sensor 140, thus reducing the layout difficulties for the magnetic part 130 and the magnetic sensor 140.

[0038] As in Fig. 3 and Fig. As shown in Figure 4, in some embodiments one of the magnetic part 130 and the magnetic sensor 140 is attached to the lens body 112, and the other of the magnetic part 130 and the magnetic sensor 140 is attached to the focusing lens tube 111. When the focusing element 120 rotates, the magnetic part 130 moves relative to the magnetic sensor 140 along the optical axis AA. That is, the magnetic part 130 is attached to the lens body 112 and the magnetic sensor 140 is attached to the focusing lens tube 111, or the magnetic sensor 140 is attached to the lens body 112 and the magnetic part 130 is attached to the focusing lens tube 111. For example, the magnetic part 130 can be attached to the lens body 112 by gluing, threaded connection, snap connection, press connection, etc., and the magnetic sensor 140 can be attached by gluing, threaded connection, snap connection, press connection, etc.be attached to the focusing lens tube 111.

[0039] In comparison to the transmission element 180, the dimensions of the lens body 112 and the focus lens tube 111 are relatively larger, providing sufficient space for the arrangement of the magnetic part 130 and the magnetic sensor 140, thus reducing the layout difficulties for the magnetic part 130 and the magnetic sensor 140.

[0040] The magnetic sensor 140 detects the linear movement of the lens body 112 in real time by monitoring changes in the magnetic field of the magnetic part 130, thus quickly and accurately obtaining the real-time position of the element 120 to be focused. Compared to the rotational amplitude of the focusing element 120, the linear movement amplitude of the lens body 112 is typically smaller, thereby reducing the detection range of the magnetic sensor 140 and increasing the detection speed. Furthermore, the surfaces of the lens body 112 and the focusing lens tube 111 are relatively large, providing ample space for mounting the magnetic part 130 and the magnetic sensor 140, which allows for greater flexibility in their positioning.

[0041] As in Fig. As shown in Figure 4, in some embodiments a receiving recess 130a is defined in the outer circumferential wall of the lens body 112, in which the magnetic part 130 is mounted. This facilitates assembly and increases the contact area between the magnetic part 130 and the lens body 112, thereby improving the reliability and stability of the connection between the magnetic part 130 and the lens body 112.

[0042] Optionally, the magnetic part 130 is mounted inside the receiving recess 130a to prevent the magnetic part 130 from protruding from the lens body 112 and colliding with other parts such as the focusing lens tube 111.

[0043] Optionally, the magnetic part 130 protrudes from the lens body 112 so that the magnetic field of the magnetic part 130 is shielded as little as possible, which benefits the magnetic sensor 140 when detecting the magnetic signal of the magnetic part 130.

[0044] As in Fig. As shown in Figure 4, in some embodiments the magnetic part 130 is attached to an end of the lens body 112 that protrudes from the focusing lens tube 111. This has less of an impact on the extension and retraction of the lens body 112, and the magnetic part 130 is less likely to collide with the focusing lens tube 111 during the extension and retraction of the lens body 112.

[0045] In some embodiments, the magnetic part 130 and the magnetic sensor 140 are spaced apart along a reference axis BB, wherein the reference axis BB is perpendicular to and intersects the optical axis AA to avoid interference between the magnetic part 130 and the magnetic sensor 140. Furthermore, the change in distance between the two is relatively linear, regardless of whether the magnetic part 130 and the magnetic sensor 140 rotate or move relative to each other, resulting in a relatively linear magnetic signal detected by the magnetic sensor 140.

[0046] In some embodiments, the magnetic part 130 is attached to the focusing element 120 or the lens body 112, and the magnetic sensor 140 is attached to the focusing lens tube 111. Generally, the volume of the magnetic sensor 140 is larger than that of the magnetic part 130. Attaching the magnetic part 130 to the movable focusing element 120 or lens body 112 has less impact on the focusing element 120 or the lens body 112. Since the magnetic sensor 140 must be connected with cables, attaching it to the fixed focusing lens tube 111 is advantageous for routing the cables.

[0047] As in Fig. As shown in Figure 5, in some embodiments the focusing device 100 also includes a distance sensor 160, a drive element 150, and a control module 170.

[0048] The distance sensor 160 is used to measure the projection distance of the focus lens 110, where the projection distance is the distance d between the focus lens tube 111 and the projection plane. The distance sensor 160 can be, for example, a time-of-flight (TOF) camera or similar device.

[0049] The drive element 150 is connected to the focusing element 120 and serves to drive the rotation of the focusing element 120. The drive element 150 can, for example, be a motor. The drive element 150 can rotate the focusing element 120 via a gear drive or drive the focusing element 120 via pulleys or other conventional methods.

[0050] The control module 170 is electrically connected to the drive element 150, the distance sensor 160, and the magnetic sensor 140. The control module 170 can rotate the drive element 150 forward, backward, or stop it. The control module 170 can also retrieve the distance value measured by the distance sensor 160 and the magnetic field detected by the magnetic sensor 140.

[0051] The control module 170 outputs a corresponding target magnet signal based on the projection distance and controls the rotation of the drive element 150 so that the magnetic signal detected by the magnetic sensor 140 corresponds to the target magnet signal. Automatic focusing can be achieved by arranging the control module 170 and the drive element 150 together.

[0052] Since the movement state of the lens body 112 can be monitored in real time by the magnetic sensor 140, there is no deviation in the focus position, thus avoiding errors that can occur in conventional optocoupler focusing solutions due to backlash in the drive motor or gear drives, resulting in high focus accuracy.

[0053] In some embodiments, the magnetic part 130 comprises, but is not limited to, at least one magnet and one magnetic alloy element. The magnetic sensor 140 comprises, but is not limited to, one or more linear tunnel magnetic resistance sensors, linear Hall sensors, anisotropic magnetic resistance sensors, and giant magnetic resistance sensors. It is understood that the aforementioned sensors can all be combined with the magnetic part 130 to achieve a good detection effect, which is conducive to precise focusing. Among these, the linear tunnel magnetic resistance sensor and the linear Hall sensor are preferred. Both the linear tunnel magnetic resistance sensor and the linear Hall sensor measure the linear change in distance of the magnetic part 130 relative to the sensor via the change in magnetic flux density.

[0054] In a second aspect of the embodiments of the present application, a projection device 300 is provided. As in Fig. Figure 6 shows that the projection device 300 comprises the focusing device 100 and an optical component 200, wherein the lens body 112 is arranged at the light exit side 210 of the optical component 200. The optical component 200 can, for example, comprise a light source, an imaging element, etc. The light source type can be LED, laser, lamp, etc., and the imaging element type can be DLP (Digital Light Processing), 3LCD (Three-Panel LCD), LCoS (Liquid Crystal on Silicon), etc.

[0055] The embodiments described above are only preferred embodiments of the present application and do not limit the scope of protection of the present application. All equivalent structural transformations carried out under the concept of the present application using the description and drawings of the present application, or the direct / indirect application in other related technical fields, are included in the scope of protection of the present application.

Claims

[1] A focusing device (100), characterized by , that it includes: a focus lens (110) comprising a focus lens tube (111) and a lens body (112); wherein the lens body (112) has an optical axis (AA) and the lens body (112) is movably arranged in the focus lens tube (111) along the extension direction of the optical axis (AA); a focusing element (120) which is rotatably arranged about the optical axis (AA) on the focusing lens tube (111) and engages with the objective body (112); wherein the focusing element (120) can move the objective body (112) along the extension direction of the optical axis (AA) when rotated and the objective body (112) does not rotate relative to the focusing lens tube (111); a magnetic part (130); and a magnetic sensor (140) for detecting the magnetic signal of the magnetic part (130); where one of cases 1 and 2 is fulfilled, In case 1: one of the magnetic part (130) and the magnetic sensor (140) is fixedly arranged relative to the focusing element (120), and the other of the magnetic part (130) and the magnetic sensor (140) is fixedly arranged relative to the focusing lens tube (111); and In case 2: one of the magnetic part (130) and the magnetic sensor (140) is fixedly arranged relative to the lens body (112), and the other of the magnetic part (130) and the magnetic sensor (140) is fixedly arranged relative to the focus lens tube (111). [2] The focusing device (100) according to claim 1, wherein in case 1, one of the magnetic part (130) and the magnetic sensor (140) is arranged on the focusing element (120), and the other of the magnetic part (130) and the magnetic sensor (140) is arranged on the focusing lens tube (111); the magnetic part (130) is configured to rotate about the optical axis (AA) when the focusing element (120) is rotated relative to the magnetic sensor (140). [3] The focusing device (100) according to claim 1 or 2, wherein, if the magnetic part (130) is fixedly arranged relative to the focusing element (120) and the magnetic sensor (140) is fixedly arranged relative to the focusing lens tube (111), the magnetic part (130) is directly or indirectly connected to the focusing element (120), and the magnetic sensor (140) is directly or indirectly connected to the focusing lens tube (111); or when the magnetic part (130) is fixedly arranged relative to the focusing lens tube (111) and the magnetic sensor (140) is fixedly arranged relative to the focusing element (120), the magnetic part (130) is directly or indirectly connected to the focusing lens tube (111), and the magnetic sensor (140) is directly or indirectly connected to the focusing element (120). [4] The focusing device (100) according to claim 1, wherein in case 2, one of the magnetic part (130) and the magnetic sensor (140) is arranged on the lens body (112), and the other of the magnetic part (130) and the magnetic sensor (140) is arranged on the focusing lens tube (111); the magnetic part (130) is configured to move along the optical axis (AA) when the focusing element (120) is rotated relative to the magnetic sensor (140). [5] The focusing device (100) according to claim 1, wherein in case 2, the magnetic part (130) is arranged on the lens body (112) and the magnetic sensor (140) is arranged on the focusing lens tube (111); wherein an outer circumferential wall of the lens body (112) is provided with a receiving recess (130a) and the magnetic part (130) is arranged in the receiving recess (130a); or wherein the magnetic part (130) is arranged at one end of the lens body (112) which protrudes from the focusing lens tube (111). [6] The focusing device (100) according to any one of claims 1 to 5, wherein the magnetic part (130) and the magnetic sensor (140) are spaced apart along a reference axis (BB), and the reference axis (BB) is perpendicular to the optical axis (AA) and intersects the optical axis (AA). [7] The focusing device (100) according to one of claims 1 to 4, wherein the magnetic sensor (140) is arranged on the focusing lens tube (111). [8] The focusing device (100) according to any one of claims 1 to 5, wherein the focusing element (120) is provided with a spiral groove (120a) whose axis coincides with the optical axis (AA), and the focusing device (100) further comprises a transmission element (180) which is connected to the lens body (112) and is arranged to slide in the spiral groove (120a). [9] The focusing device (100) according to any one of claims 1 to 5, further comprising: a distance sensor (160) which is used to measure a projection distance of the focus lens (110); a drive element (150) that engages with the focusing element (120) to rotate the focusing element (120); and a control module (170) that is electrically connected to the drive element (150), the distance sensor (160), and the magnetic sensor (140); wherein the control module (170) is configured to output a corresponding target magnet signal based on the projection distance and controls the drive element (150) so that the magnetic signal detected by the magnetic sensor (140) corresponds to the target magnet signal. [10] A projection device (300) comprising: the focusing device (100) according to any one of claims 1 to 9; and an optical component (200); wherein the lens body (112) is arranged at a light exit side (210) of the optical component (200).

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